Add full support for TerrainTypes

[atomicptr]

Seems I forgot to add some parts of this feature:

In the desert.tsx file are some not used properties:

<tile id="0" terrain="0, 0, 0, 1" />
<tiled id="1" terrain="0, 0, 1, 1" />
....

[atomicptr]

there is also a probability tag for tile.