[Finishes #78333634] Implements User/Org association

And a lot of various other improvements

[#78333634] API now allow end-to-end creation of a new User-Org association (with Role)
[#78333634] More tests and finalized structure of the UserOrgAssoc inner class
[#78333634] Completed deserialization from MongoDBObject, started to work on permissions and initial API tests
[Starts #78333634] Associates a User with multiple organizations and roles