Add include guard to ITerrainObserver.h
Disable the use of EmberPagingSceneManager.

 - Remove EmberPagingSceneManager from the build
 - Create dummy implementations for the needed scene manager related classes.
 - Use Ogre default scene manager or OctreeSceneManager if loaded.
 - Comment out RaySceneQueries which depend on World Geometry being
   supported by the scene manager in AvatarTerrainCursor and
   ThirdPersonCameraMount
Rename ISceneManagerAdapter

 - ISceneManagerAdapter is responsible for managing terrain related
   data, therefore rename it to ITerrainAdapter.
Move main menu scene manager instantiation

 - Remove instantiation of scene manager for the main menu from
   OgreSetup.
 - Directly create it in EmberOgre instead.
 - Rename scene manager and camera objects in EmberOgre.
Change terrain intersection testing.

- Introduce rayIntersects to ITerrainAdapter to let the terrain
  implementation decide how to check for ray collisions.
- Use rayIntersects instead of RaySceneQueries in AvatarTerrainCursor,
 EntityWorldPickListener and ThirdPersonCameraMount.
Use ITerrainAdapter to query GrassFoliage height
Use ST_EXTERIOR_REAL_FAR to create scene manager