[Dovecot] Replicator updates

[Timo Sirainen]

Some new features in hg:

 - replicator now correctly saves/restores state on exit/startup. it won't immediately start resyncing everyone now always.
 - if sync fails for user, retry in 5 minutes
 - doveadm replicator status: Give overview of replication status
 - doveadm replicator status <usermask>: Show users' replication status
 - doveadm replicator replicate [-p <priority>] <usermask>: Replicate users now.

replication_full_sync_interval was also changed to 24h by default. I was thinking that with that and a nightly cronjob running "doveadm replicator replicate '*'" the full syncs could only be done during night times.