Python API for ingestion - Marshmallow schema for Relationship (load + dump)

[krzysztof]

This should be a module which accepts the Event payload JSON and writes to the DB.

Marshmallow solution:

[ScholixRelation JSON] -> scholix_marshmallow.load(json_payload) -> [DB Object]
[DB object] -> scholix_marshmallow.dump(db_obj) -> [ScholixRelation JSON]

[krzysztof]

DB -> JSON is not there because we will not need it, but ES response -> Scholix JSON is needed (currently done without marshmallow schema).