Disable the use of EmberPagingSceneManager.

 - Create dummy implementations for the needed scene manager 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

Most of the changes are preliminary and not intended to stay like this.
The intention is to have something which works for now.
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