Rename edentity to customentities

This fixes the fact that the name of the singular type is plural, but
the name of the plural array is singular. Which has always annoyed me,
too. Also this makes it more clear that custom entities don't have much
to do with the editor.

desktop_version/src/main.cpp

@@ -32,7 +32,7 @@
 scriptclass script;
 
 #ifndef NO_CUSTOM_LEVELS
-std::vector<CustomEntity> edentity;
+std::vector<CustomEntity> customentities;
 customlevelclass cl;
 # ifndef NO_EDITOR
 editorclass ed;