- add_update_appointment handles the slot count and also keeps a copy of the appointment uuid and slots taken.
- gatekeeper.appointments is turned to a dict uuid:slots so appointment updates can be computed with no further data
- deleting appointment will also allow to update the slot count with no further data from both the Watcher and the Responder
Following the same apporach as the Inspector, the gatekeeper now raises exceptions depending on the error encountered.
Also generalises `identify_user` so it can be used with any kind of user-signed message.
Finally lifts the restriction of having available slots on `identify_user` (that only applied to `add_appointent`).
+ Users need to be registered in order to send appointments (free registration for now)
+ The tower gives them a number of appointments to work with
+ Non-registered users and users with no enough appoitnemnts slots return the same error (to avoid proving)
- Authentication does not cover get_* requests yet
- No tests
- No docs
- Adds register endpoint in the API
- Adds the Gatekeeper to keep track of registered user and allow/reject access
- Adds registration errors
- Updates API unit tests
- Refactors some methods of the API to reduce code replication
