Fix #5344 - OAuth NotImplemented exception

Fix #5344 - OAuth NotImplemented exception

This introduces a migration which adds a dummy Client, RequestToken
and AccessToken. These are used when an invalid request comes in,
instead of bailing early, it needs dummy data to prevent timing
attacks.

This then implements the methods which get the IDs of the dummy
objects. If these are changed in the future a migration which checks
for the previous dummy object should be created and updates them to
reflect the new IDs/tokens.