Many fixes to OBJImporter

This topic fixes a few issues and adds a test executable
that can be used to convert obj files to vtp more easily.

The issues fixed are

1) having a map_Kd without a texture name cause a crash

2) having materials in the mtl file that were not used
resulted in geometry and parts missing from the output

3) having material names with spaces in them caused
the material not to be recognized

4) some packages use map_kd instead of map_Kd causing
textures to not be found.