Add model ctor
Merge branch 'new3dapi' of https://github.com/libgdx/libgdx into new3dapi
Generate ids for materials if none given, very basic ModelBuilder class, use bits for VertexAttributes#Usage, fix bullet tests.
Remove unneed initialization
Add very basic cylinder shape
Merge pull request #317 from xoppa/new3dapi

New3dapi, various changes