More reorganization.

Main effect is to put terrain.cfg and terrain-graphics near each other
as eleazar requested.

data/_main.cfg

@@ -1,8 +1,6 @@
 {themes/}
-{core/macros/}
 {core/}
 {hardwired/}		# Locations under here are wired into the C++
-{terrain-graphics/}
 {campaigns/}
 
 [binary_path]

data/core/_main.cfg

@@ -0,0 +1,19 @@
+# Main purpose of this file is to ensure that macros get read in first.
+{core/macros/}
+{core/abilities.cfg}
+{core/about.cfg}
+{core/amla.cfg}
+{core/editor-groups.cfg}
+{core/fonts.cfg}
+{core/help.cfg}
+{core/hotkeys.cfg}
+{core/items.cfg}
+{core/multiplayer.cfg}
+{core/names.cfg}
+{core/schedules.cfg}
+{core/special-notes.cfg}
+{core/team-colors.cfg}
+{core/terrain.cfg}
+{core/terrain-graphics/}
+{core/traits.cfg}
+{core/units.cfg}