* Handle mailbox moves/renames
* plugin segfaults when it is unconfigured
* imap-metadata segfaults when dealing with server annotations
* imap-annotatemore seems to fail in some cases where imap-metadata succeeds
* Split entry name validation between frontend and backend:
  - imap-annotatemore checks the draft specific parts and removes them from the string
  - backend checks according to RFC 5464 and builds entry struct
  - Frontends validate entry struct against their specs
