New terrain system - please test!

The default terrain shader does not come with any splatmap or procedural splatting. The reason for this is that you usually want to customize it anyway, and so you have to write the material distribution yourself.

The same applies for detailmaps, since there are a lot of possibilities.

Right now the terrain itself does provide any collision mesh, but you can use the BulletHeightfieldMesh for collisions.