Really (?) fixed cursor items causing graphics corruption with building tools.

Note that rewriting DrawTileToolCursor to derive from QGraphicsItem didn't
fix anything.
Fiddling with building tile tools.

DrawTileTool captured tiles work with regions of tiles, not just a rectangle.

DrawTileTool will erase in the shape of captured tiles with CTRL.

Status text reflects the actions of the tools more precisely.

DrawTileToolCursor uses MapRenderer::drawTileSelection rather than drawing
a polygon.
Implemented cut/copy/paste of building tiles.
BuildingTileModeScene tracks the level with the force-not-empty layer.
Allow painting furniture tiles in building tile-edit mode.

Added the Furniture Dock.  Selecting a furniture tile in the Furniture Dock
sets the DrawTilesTool's capture tiles.

This let to some bug fixing with the use of regions and FloorTileGrid.
Played around with highlighting individual layers by dimming all the others.
Added BaseFloorEditor, BuildingRenderer classes, etc.

Adding support for both orthogonal and isometric building views.
The goal is to allow the building tools to work the same in both orientations.

BuildingRenderer is analogous to Tiled::MapRenderer; this class renders
building objects and handles coordinate transformations.

BuildingObject gained calcShape() to return a polygon (in tile coords) that
is used to render the object.
Added BuildingMap class.

BuildingMap handles all the Building -> Tiled::Map monkey business.
All the work it does used to be done by BuildingTileModeScene.
The nice thing about BuildingMap is it does delayed updates.