@ fixed bug that caused a question message to save the map appear on closing after saving the map

@ working on NumericTextbox versions with up/down buttons and dropdown lists

- Fixed bug that allowed pasting geometry in visual mode (and the geometry becomes erroneous)

- Highlight and selection colors are now hidden while dragging textures.

- Progressive undo/redo system (much faster and up to 1000 undo/redo levels) Please note that several plugin functions and properties have changed.
- Some small optimizations in the classic 2D rendering (cached linedef flags, reduced some unneeded redrawing)

@ Changed the MapSet to work with arrays instead of linkedlists. Because the index is now know for each element and can be retrieved in O(1) efficiency it has become a property (Index) for all map elements. GetIndexFor* functions have been removed. Get*ByIndex are now also of O(1) efficiency.

Replacing can now be made undone

Added variable "skyflatname" as a game configuration item. It is used to ignore false positives when checking for missing textures. Updated all the game config files to make use of this feature.

- Added HighlightedObject property to the EditMode class, the object returned depends on the editing mode and the current highlight
- Exposed several properties in the ClassicMode class

Fixed updating used textures when pasting so that they are loaded and displayed on the geometry surface

- Little optimization in MarkSelected... functions

- Some minor interface polishing

- Fixed potential crash and "ghost thing" left-over after cancelling pasted things

Removed option "keep selection" from Find & Replace dialog (not sure why I put that there, it doesn't do anything)