Merge pull request #315 from xoppa/new3dapi

New3dapi
modified model
Merge branch 'new3dapi' of https://github.com/libgdx/libgdx into new3dapi
Merge pull request #316 from xoppa/new3dapi

revert
Merge branch 'new3dapi' of https://github.com/libgdx/libgdx into new3dapi
added ModelInstance :D, fixed up tests, bullet has issues with lighting, not sure why
node translation/rotation/scale are initialized to sane values
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.