Add vtkOBJImporter class and associated test.
Allow importing material info from *.mtl files that are associated with *.obj files.
Handle more cases of .obj file format, such as interleaved geometry defintions (switching back and forth between actors and multiple polydata)
fetch test data and verify md5 checksum.
example of imported data from MiG-35.obj + MiG-35.obj.mtl files: