VOMDL checking

This major release adds 2 new checking level:

Verification that all types and roles read from within the annotation block match those of the VODML.
Verification that the structure of the mapped instances match the VODML classes

1.1: Merge pull request #2 from ivoa/feature/check_types_and_roles

The validator has a new end point that can check that all dmtype and dmrole referenced in the mapping block are known by mapped models. It does not care of the class structures This checking only works with the Meas/Coord/ivoa models, other models are ignored.