Add support for mapping terms to licensed or restricted use ontologies

[simonjupp]

To increase coverage ontology coverage OTAR and GWAS requires access to medical terminologies, coding standards e.g. OMIM, SNOMED-CT, MESH, MEDDRA, NCIT, ICD. We can’t readily make them available in OLS as they are either unavailable in a suitable format (like OWL), or there are constraints on the license that prevent us from publically hosting them. We should however be able to make them searchable through Zooma by only loading the labels and synonyms. Users will be able to map to these terminologies through Zooma and translate terms to public ontologies using OxO.