Reorganized renderer (again)

-Added TilesetLibrary
-TextureLibrary only manages textures (no more tilesets)
-Render has now an object renderer
-VAOs are now stored into their tileset
-Every module now uses render_window rather than #render_target
Joints now use tilesets
Merge pull request #102 from GL-MPRI-2014/new_renderer

New renderer