MP Lobby: base resolution selection on window width not height

[ci skip]

Height isn't the problem. The default lobby can display fine even at 600 px h. Width is
the problem the default layout faces at low resolutions, and it was quite odd to have a
really wide window use the low resolution layout, despite there obviously being enough
horizontal space to fit the sidebar.

changelog.md

@@ -21,6 +21,7 @@
    * Ensure the chat widget remains the correct size even after a window resize.
    * Custom MP game names are now capped at 50 characters.
    * Restored Era info to main MP game display.
+   * Improved the resolution selection criteria for the MP Lobby.
  ### Miscellaneous and bug fixes
    * Removed misleading tooltip text stating registered nicknames are optional for
      the official MP server.

data/gui/window/lobby_main.cfg

@@ -555,7 +555,7 @@
 	# Low resolution
 	#
 	[resolution]
-		window_height = 600
+		window_width = 800
 		definition = "borderless"
 
 		{GUI_WINDOW_FULLSCREEN}
@@ -779,7 +779,7 @@
 	# Default resolution
 	#
 	[resolution]
-		window_height = 660
+		window_width = 1000
 		definition = "borderless"
 
 		{GUI_WINDOW_FULLSCREEN}