Add inheritance and onset to bioentity/{type}/{id}

[kshefchek]

Adds inheritance and onset to bioentity/{type}/{id}. Note that I'm switching our default scigraph instance to our data graph and pulling all outgoing edges (this may scale poorly). An alternative would be to allow scigraph neighbors to accept multiple relationship types. I'm also overloading BioObject with these new fields - alternatively, we could create a disease object and dynamically pass api.models into marshal_with based on the type param.

[deepakunni3]

I like the idea of dynamically passing api.models into marshal_with based on type. We can probably have that as part of another PR.

[kshefchek]

How does this look? https://github.com/biolink/biolink-api/pull/243/commits/a3294aecda368515fb82a02523a00748eac14893

[deepakunni3]

Yes, that looks great. For a second there I thought the switch should apply to other types too, but then realized that bio_object pretty much applies to all the remaining types. 👍