If re-establish a connection don't print the room history again.
In case there there happened nothing at all since we got the room
history on the last connection.
And in case there were no new messages during the time we have been
disconnected.
Instead of printing the room history again we now print 'Re-established
Connection'.
This adds a bit of overhead since we save the timestamp upon every MUC
message.
See: https://github.com/profanity-im/profanity/issues/704
