added TextureManager; works, but not tested with current projects
# GB_Model no longer load BB3D if mesh isn't available
# GB_Model no longer tried to load material file if file doesnt exist
# GB_Model loading texture control statement works correctly
# GB_Model no longer rendered if mesh doesn't exist
small changes in test data
remove simples meshes, problem with static variables (cannot be used in other modules like GBTA)
- texture manager now included
- fixed problems with GB_Model constructor when mesh, material or texture wasn't found
- GB_Loader::LoadTextureFile still uses glTexImage2D for creating texture images --> find a way to use gluBuild2DMipmaps
added todo