Default theme uses 'classic' dir, Classic uses 'legacy'

Reverts a decision from commit 10b7cd63f5
in order to both make the Classic theme backportable to 1.12 and
eliminate an unnecessary complication for UMC.

At some point in the future, the Default theme will replace Classic when
the rumored UnitBox theme becomes the default, so I'd say naming its
directories "classic" makes sense, while the current Classic theme is
the "legacy" classic.

If we hadn't gotten stuck with Default using "classic" dirs in 1.12
there would be no need for any of this irritating nonsense.

data/themes/_initial.cfg

@@ -183,7 +183,7 @@
     # use right pane with a smaller minimap
     [change]
         id=minimap-panel
-        image=themes/default/minimap-800.png
+        image=themes/classic/minimap-800.png
         rect="842,=+6,+181,+177"
     [/change]
 
@@ -229,7 +229,7 @@
     [panel]
         id=minimap-panel
         #ref=terrain-description-box-botleft
-        image=themes/default/minimap.png
+        image=themes/classic/minimap.png
         rect="=,=+6,+181,+265"
         xanchor=right
         yanchor=fixed

data/themes/classic.cfg

@@ -34,7 +34,7 @@
 
         [panel]
             id=top-panel
-            image=themes/classic/top-bg.png
+            image=themes/legacy/top-bg.png
             ref=screen
             rect="=,=,=,+26"
             xanchor=top
@@ -81,21 +81,21 @@
         # rightside panel
         [panel]
             id=top-right-panel
-            image=themes/classic/rightside.png
+            image=themes/legacy/rightside.png
             rect="+0,=+0,1024,+284"
             xanchor=right
             yanchor=fixed
         [/panel]
         [panel]
             id=middle-right-panel
-            image=themes/classic/rightside-bg.png
+            image=themes/legacy/rightside-bg.png
             rect="=,+0,=,+421"
             xanchor=right
             yanchor=top
         [/panel]
         [panel]
             id=bottom-right-panel
-            image=themes/classic/rightside-bottom.png
+            image=themes/legacy/rightside-bottom.png
             rect="=,+0,=,768"
             xanchor=right
             yanchor=bottom
@@ -148,7 +148,7 @@
 
         [panel]
             id=turn-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             ref=actions-menu
             rect="+5,=+1,+80,+19"
             xanchor=fixed
@@ -156,35 +156,35 @@
         [/panel]
         [panel]
             id=gold-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             rect="+5,=,+76,="
             xanchor=fixed
             yanchor=fixed
         [/panel]
         [panel]
             id=villages-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             rect="+5,=,+71,="
             xanchor=fixed
             yanchor=fixed
         [/panel]
         [panel]
             id=units-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             rect="+5,=,+71,="
             xanchor=fixed
             yanchor=fixed
         [/panel]
         [panel]
             id=upkeep-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             rect="+5,=,+90,="
             xanchor=fixed
             yanchor=fixed
         [/panel]
         [panel]
             id=income-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             rect="+5,=,+85,="
             xanchor=fixed
             yanchor=fixed
@@ -193,7 +193,7 @@
         #  {COUNTDOWN_THEME}
         [panel]
             id=timeout-panel
-            image=themes/classic/status-bg.png
+            image=themes/legacy/status-bg.png
             rect="+5,=,+90,="
             xanchor=fixed
             yanchor=fixed

data/themes/default.cfg

@@ -45,7 +45,7 @@
 
         [panel]
             id=top-panel
-            image=themes/default/menubar.png
+            image=themes/classic/menubar.png
             ref=screen
             rect="=,=,=,+27"
             xanchor=top
@@ -65,7 +65,7 @@
 
         [panel]
             id=sidebar-panel
-            image=themes/default/sidebar.png
+            image=themes/classic/sidebar.png
             rect="+0,0,1024,768"
             xanchor=right
             yanchor=top

data/themes/editor.cfg

@@ -42,7 +42,7 @@
         ####### Menu Bar
         [panel]
             id=top-panel
-            image=themes/default/menubar.png
+            image=themes/classic/menubar.png
             ref=screen
             rect="=,=,1024,+27"
             xanchor=top
@@ -50,7 +50,7 @@
         [/panel]
         [panel]
             id=top-panel-right
-            image=themes/editor/default/menubar_rightside.png
+            image=themes/editor/classic/menubar_rightside.png
             rect="+0,=,+10,+27"
             xanchor=right
             yanchor=fixed
@@ -185,7 +185,7 @@
         ####### Upper Toolbar - Left Side
         [panel]
             id=replay-panel
-            image=themes/editor/default/toolbar.png
+            image=themes/editor/classic/toolbar.png
             ref=top-panel
             rect="=,+0,+833,+41"
             xanchor=left
@@ -193,7 +193,7 @@
         [/panel]
         [panel]
             id=replay-panel-right
-            image=themes/editor/default/toolbar_rightside.png
+            image=themes/editor/classic/toolbar_rightside.png
             rect="+0,=,+10,+41"
             xanchor=right
             yanchor=fixed
@@ -470,7 +470,7 @@
         ####### Game Map
         [panel]
             id=border-top
-            image=themes/default/mapframe_top.png
+            image=themes/classic/mapframe_top.png
             ref=replay-panel
             rect="0,+0,708,+10"
             xanchor=left
@@ -478,7 +478,7 @@
         [/panel]
         [panel]
             id=border-top-right-corner
-            image=themes/default/mapframe_toprightcorner.png
+            image=themes/classic/mapframe_toprightcorner.png
             rect="708,=+0,+135,+10"
             xanchor=right
             yanchor=fixed
@@ -495,7 +495,7 @@
 
         [panel]
             id=border-right
-            image=themes/editor/default/mapframe_rightside.png
+            image=themes/editor/classic/mapframe_rightside.png
             rect="+0,=+0,+10,768"
             xanchor=right
             yanchor=top
@@ -513,7 +513,7 @@
         ################################## Rightside Panel
         [panel]
             id=top-right-panel
-            image=themes/default/sidebar.png
+            image=themes/classic/sidebar.png
             ref=screen
             rect="843,0,1024,768"
             xanchor=right
@@ -525,7 +525,7 @@
         ####### Main Toolbar
         [panel]
             id=tools-panel
-            image=themes/editor/default/tools.png
+            image=themes/editor/classic/tools.png
             ref=terrain-description-box-botleft
             rect="=-7,+3,+181,+155"
             xanchor=right
@@ -792,7 +792,7 @@
 
         [panel]
             id=palette-top-panel
-            image=themes/editor/default/palette_top.png
+            image=themes/editor/classic/palette_top.png
             ref=menu-editor-terrain
             rect="843,+5,1024,+45"
             xanchor=right
@@ -801,7 +801,7 @@
 
         [panel]
             id=palette-panel
-            image=themes/editor/default/palette.png
+            image=themes/editor/classic/palette.png
             rect="=,+0,=,768"
             xanchor=right
             yanchor=top