Fixed MapImageManager not updating BmpBlender before rendering.
BmpToolDialog gained "Show BMP-generated tiles" option.
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.
Optimized BmpBlender's use of getNeighbouringTile().
BmpBlender delays calling initTiles() until needed.
BmpBlender::updateWarnings() now checks for unknown pixel colors.

Having unknown pixels in BMPs prevents blending occurring and it isn't
obvious to the user why that is happening.
Fixed LUA script changes to BMPs not updating the BMPs correctly.
Add "Blends" tab to BmpToolDialog.
Added LuaMapsDialog to run a LUA script on chosen files in a directory.
Multiple WorldEd projects can be specified in the Preferences.
Added LuaWorldDialog for running a LUA script on all the cell maps in a WorldEd project.
Fixed Lua scripts not being able to erase tiles.

PainTileLayer was changed so that it can paint empty cells.
Added Lua methods Map:reloadRules() and Map:reloadBlends().
BmpToolDialog displays blend details in a label.

Details used to be in a MixedTilesetView header.
ChangeBmpRules/ChangeBmpBlends destructors delete unused data.
Disable the debug-only 1/2 second delay when loading tilesets.
Fixed tooltips in PreferencesDialog.
Choosing "Run Script..." in LuaConsole defaults to the last-used script.
Added 'scriptDirectory' global for Lua scripts.
Missed commit for #include in luatiled.cpp.