Add comment to TerrainPageSurfaceLayer
Add TerrainMaterialGeneratorEmber

This MaterialGenerator can be used by the Ogre Terrain component to use
the materials generated by Ember.
Use Ember materials for Ogre terrain.

Enables usage of OgreTerrainMaterialGeneratorEmber which causes the Ogre
Terrain component to use the materials generated by Ember.

The terrain looks acceptable now, there are a few material-related
graphical artifacts remaining though(E.g. shadows and lighting does not
look very good).
Set some Ogre Terrain options for testing.