started group functionality. Added ability to join and scan groups.
Can now join multiple groups with one command
Changed user list in Group to a set. Changed grouplist in server to a set
Added group messaging
Changed list of groups back to an arraylist for easy access to main group. Added main group and add all users to main group
added the ability to leave groups (including the main one)
Merge pull request #1 from Steven-Ireland/groups

Groups