Add external disease vocabularies to DO, even without hierarchy

The current monarch interface for diseases requires disease ids to be present in our ontology (monarch.owl) in order for us to (1) display the label and (2) do the proper aggregation of various data annotated to different disease ids.

One way to achieve this is to firstly add all the external disease ids into an uncategorized section of the ontology so that they are at least a child of "disease", but don't necessarily have other relationships. Then, as the hierarchy and class-mappings get solved, they will find their new location. But this would then allow us to resolve any disease id in our system, and as the ontology gets fixed, our interface would "magically" get fixed.