Fixed CellView not centering correctly due to adjacent map loading.

Centering on sceneRect().center() was buggy due to asynchronous loading of
adjacent maps changing the sceneRect().
Further attempts to fix CellScene painting.
Ported stuff from TileZed.
Lots in adjacent maps are now displayed.
Fixed 0_Floor* tiles not being shown under Lots in adjacent maps.
SubMapTool map-highlight-item tooltip shows the map name.
Reverted change putting heightmap into .lot files since it isn't used yet.
Improvments to adjacent maps.

1) Lots in adjacent maps are shown.
2) Adding/removing/moving lots in adjacent cells updates the CellScene.
3) Resizing the world updates adjacent cells.
Lots in an invalid position are displayed with a different color.

Currently, this only checks for RoomDef rects outside a map's bounds.
It should also check for tiles being cut off.
Ported BuildingFloor::hasUserTiles() from TileZed.
Removed unused code.