WriteSpawnPointsDialog default filename is spawnpoints.lua.
GotoDialog: added missing colons in label.
BaseHeightMapTool: Pass 'parent' argument to base class constructor.
Added command to write an image file with buildings painted in.

Lemmy wanted the world BMP(s) with RoomDefs painted in.
Fixed cell thumbnails not loading if a cell doesn't have a cell map.
Fixed MapImageManager not running BmpBlender before rendering.
BmpBlender optimizations.
BmpBlender warns if a map has unknown BMP colors.
Force non-empty level 0 in MapComposite to deal with BMP images.

If a map is all BMP with no user tiles, then BmpBlender won't get called
due to the BMP layers initially being empty/non-existent.
Experiment with normalizing rule tilenames.

This should be done, but changes which random tiles are chosen.
Old: Pick a random tile/alias, then pick a random tile from the alias (if any).
New: Pick a random tile from aliases-already-resolved list of tiles.
Made SpawnToolDialog buttons autoRaise=true.
Experiment with copying image data to maps instead of blending in BMPToTMX.
Ported MapComposite.mShowBmpTiles stuff from TileZed.
Ported BmpBlender "tile name -> tile pointer" rewrite from TileZed.
Rewrote BMPToTMX to use BmpBlender.

BmpBlender was based on the code in BMPToTMX, but it was never a good idea
to have the same code in 2 places.  Plus BmpBlender is a lot faster due to
recent changes.

Fixed reportUknownColors() not doing anything due to mImages being cleared
right before calling it.

The unknown-colors code now correctly checks for unknown colors in each BMP
image separately.  If a color in the "veg" image corresponded to a "main" rule
but no "veg" rule with that color existed (or vice versa) it wouldn't be
reported.
Highlight-room-under-pointer stuff considers lot visibility.
PNGBuildingDialog draws pixels representing trees into the output image.