(NC-158) Mark params deleted

Previously when handling a class that should be deleted during a synchronization, only the class was marked deleted while the parameters were untouched, which would lead to an error in create-parameter when it tried to re-insert parameters that already existed.

As an additional precaution against this sort of bug, create-parameter is now idempotent, in that it just updates the parameter if it already exists in the database (previously it would only update if the parameter existed *and* its delete field was `true`).