Draft RFC for updating data in the registry

[woutslakhorst]

For a better understanding it can be useful to add the individual operations that can occur. After a vendor has been created, it can be:

• removed, same as revoking
• continued, new certificate with same keys but longer lifespan
• replaced, key rotation

what kind of events are needed for this. Continued could just be a sort of add-operation..

[reinkrul]

Merging in preparation to being replaced by Nuts Specification RFC 3, 4 and 5.