imap-hibernate: Properly fix hibernation The previous fix did not properly fix hibernation as the clients still dropped out of hibernate. Also the tag used was no longer following. This change will track tag changes and keeps the hibernation process going on until the user enters something else than DONE\r\ntag IDLE\r\n in same packet.

Added imap-hibernate process for gathering IDLEing imap processes. imap_hibernate_timeout setting controls how quickly the connection is moved from imap process to imap-hibernate process. Some IMAP extensions like NOTIFY, SEARCH=CONTEXT and COMPRESS aren't supported yet. There's also a new X-STATE command, which can be used to export the current IMAP connection state to a string and later on imported to get back to the original state (a quick resync feature for IMAP clients). However, this command is disabled for now due to the current code being unoptimized for untrusted input.