invalid_appointments in TowerInfo was used to stored invalid appointment responses from the tower when it was misbehaving (i.e. wrong or missing signature). However, a single item was stored since the tower is abandoned after misbehaving. data reported as invalid by the tower was not backed up.
invalid_appointments now stores the appointment rejected by the tower and reported as invalid.
misbehaving_proof stores the proof of misbehaviour by the tower (single item)
The previous approach was a bit messy with the db access and could have potential race conditions and data inconsistency
Also replaces format for f-functions for readability
