Terrain: support alternate coordinate systems. Get rid of LoadingListener for now
Terrain: remove hard dependency on shiny - can now be compiled without it (fixed function)
Render maps after *all* cells have finished loading

Still not fixing Bug #772, but at least this will allow for background loading of terrain.
Terrain: fix an embarrassing copy&paste mistake.
Terrain: moved ESM::Land load to earlier in the startup procedure

Required for background loading as we cannot load ESM::Land data from background threads.
Terrain: take cell world size into account for LOD selection
Terrain: geometry is now loaded in background threads.

TODO: background load layer textures and blendmaps.
"Distant land" setting has been removed for now (i.e. always enabled).
Include some more required Ogre headers explicitely.
Set StaticGeometry origin

Fixes an exception for coordinates far away from (0,0,0).
Terrain: decoupled Chunk from QuadTreeNode.
Terrain: destroy no longer used materials
Terrain: get rid of unneeded members
Terrain: background load blendmaps & layer textures. Refactor QuadTree update.
Bug #416: Workaround for page flipping problem
Terrain: re-added "distant land=off" path

Still a hack, but the overhead of building and traversing the quad tree appears negligible.
Bug #416: Copy framebuffer to a texture instead of not clearing

Potentially faster than the previous workaround, and should work for triple buffering too.