VIVO-843 "every time" sub-models were being lost.

The problem comes when you wrap an OntModel around a Model. Sub-models are added to the OntModel, so unless you keep the same OntModel, those sub-models get lost.

This is a kluge, rather than a fix.
Merge branch 'develop' of git+ssh://github.com/vivo-project/Vitro into develop