This is a pretty hefty commit! But essentially, I made a new editorclass
object, and moved all functions and variables that only get used in the
in-game level editor to that class. This cleanly demarcates which things
are in the editor and which things are just general custom level stuff.
Then I fixed up all the callers. I also fixed up some NO_CUSTOM_LEVELS
and NO_EDITOR ifdefs, too, in several places.
This accompanies the editor.cpp -> CustomLevels.cpp change; I'll be
splitting out the editor functions in the next commit. The name of the
include guard has been changed as well, but not anything else.
This moves editorrenderfixed(), editorrender(), editorinput(),
editorlogic(), and their associated functions to a new file named
Editor.cpp - which is exactly what it says on the tin; it stores all the
functions related to the actual in-game editor loop. Also, the existing
editor.cpp has been renamed to CustomLevels.cpp.
