QRESYNC support (VANISHED)

[vitalif]

Hi.
There's an extension here https://tools.ietf.org/html/rfc5162 which allows for fast IMAP synchronization, including UID message delete notifications (VANISHED).
It seems rather simple to support - you only need to send ENABLE QRESYNC and then watch for additional mailbox flags + VANISHED responses instead of EXPUNGE.