0.8.8a2 - Optimized Map View, rendering overhaul

MapTileItem has replaced TileItem for areas, rendering an entire layer
of tiles rather than single tiles. This drastically improves memory
usage and load times between areas, while sacrificing some performance
while the view is zoomed far out (still looking for a fix...).
CollisionItem has also been modified to be treated the same as
MapTileItem (there is no need for individual CollisionItems - they will
always be contained by Areas). DestView is still document-ignorant,
while MapView has many functions previously delegated to higher levels
reimplemented to be optimized specifically for Areas.

TileItem remains as a legacy class for the sole purpose of rendering
SheetView (adding an extra SheetTileItem class would be redundant and
would not offer much improvement).

Undo and Redo (PlaceTileCommand and PlaceCollisionCommand) are also
properly supporting the new items (PlaceTileCommand may be renamed to
PlaceMapTileCommand in order to support later tile commands not specific
to Areas).