- added basic group messaging
- now each user can only have one session at a time, mutltiple logins would replace previous session
- added basic delete function
- extracted the inbox from within user record to its own collection
- experimented with two inboxes idea, one for individual messages, the other for group. probably not a good idea

bugs:
- group messages cannot be deleted.
Merge branch 'master' of https://github.com/lysisius/im