[Fix #53] Same user cannot be connected twice

The mobwrite peerid is now random and it is also send in the command join and part.
Merge branch mobwrite-peerid

This is the base work to rely on to fix issue #53.
[fix #53] Peers join resource, not username

when need to track individual peers (meaning editors) not user, so that
the same user can be connected twice to a paper to edit it.
Merge pull request #73 from satabin/fix-53

Fix #53 Same Paper Cannot Be Connected Twice