Added tile shape groups to TileShapes.txt, no more hardcoded categories.
EnflatulatorDialog: fixed resizing faces, added roof shape.
TileShapeEditor shows the current texture when editing u/v coords.
Rendering isometric tiles done in 3D now so depth-buffer can do its job.

I was rendering the tiles with OpenGL, but in 2D orthographic perspective
which had every point on z=0.  Now I'm using the correct isometric perspective
so depth buffering works.
Changes for porting virtual tileset stuff to WorldEd.
Removed unused code.
Tile shapes can share geom/uv with another.  Added roof accent tile shapes.

Many virtual tile shapes are simply an offset copy of another. To avoid having
to recreate all the geometry/uvs for such tiles, a tile can now point to
another tile and use that tile's geometry/uvs.
EnflatulatorDialog: working on getting door/window/curtain textures.

Basic idea is to choose north/west facing direction for each tile, flatten
it into a new texture image.  Left-click picks west face, right-click picks
north face.
VirtualTilesetView tooltip shows the shape name.
Added texture tile size, shape sameAs/xform ui.