We no longer use the hardcoded objectUniform UBO name, instead, we
access the object uniforms through the new getObjectUniforms().
Because it's not possible to return a "Uniform Block" from a function
in GLSL, a large part of this change, is to replace the interface block
by a structure.
Note: getObjectUniforms() is not public, but it is used by gltfio to
access the userData field, which is also not public at the moment.
Mathias Agopian
803ce07701