Fixed issue with model not being shown.

If a model is first attached to a HiddenAttachment, and then later on
gets attached to a ModelAttachment, it would not be shown, as it would
never be set to be visible.
Remove empty "user" directory.
Fix broken GUI disabling/enabling.
Use Ogre 1.9

 - OverlaySystem is now a component, add to build and initialize it in OgreSetup
 - Scene Managers can retrieve the OverlaySystem from OgreSetup and
   register it with themselves to show overlays.
 - Add some implemented methods due to Ogre interface changes.
 - Purge includes of OgreProgressiveMesh since it was removed.
 - TODO: use QueuedProgressiveMeshGenerator from Ogre. Current state
   throws some cast exceptions in the background.
Fix Ogre macro usage for Ogre 1.9

Now it requires ';' after the macro.
Use Ogre's built-in Lod generator.
Fix rebase.
Fix LodDefinition Lua bindings
Add include guards
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.

Fix formatting in Scene.cpp
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)
Enable terrain paging using a flat terrain