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,
  MainCamera and ThirdPersonCameraMount.
- In MainCamera, a result for the RaySceneQuery is created manually if
  the ray intersects with the terrain so the listeners do not have to be
  changed.
Use ST_EXTERIOR_REAL_FAR to create scene manager
Pass ray by reference in ITerrainAdapter
Resolve some coding standard issues.
Add Ogre::Terrain and Ogre::Paging to build
Move IPageData from scene manager specific code.
Use Ogre::Terrain component with a constant height.

- Only basic support, no paging or data from Mercator yet.
- No Materials used yet, so far the terrain is a black surface.
- Move the dummy implementations to a separate directory(can be deleted
  later if unnecessary)