* aside from slight refactors there have been route changes
(/api/v1/service/ --> /api/v1/service)
* added helper little function for grabbing user and service ids
* refactored a couple of return statements
* added separate models for updates
* adjusted error handling behaviour: more general 422 is now returned
(previously 404 was used) --> hopefully leaking less information
* updates are divided into multiple queries **as of now**, mainly due to
my sqlalchemy amateurism: can't figure out how to construct a proper
multi-column-update query programatically
