Altered groupController/homeAction so a user from another instance can enter
a groups home-site.
Altered GroupController/getGroup so it returns null instead of an error
if a group does not exist.
Implemented APIs for joining a group
Added testmethods for getGroupByAuthorUri and getPersonByAuthorUri in GroupController
Added API for leaving a group i.e. unsubscribe from each member and have
each member unsubsrcibe from me
Updated baseUri retrieval
Added method to get the baseUri of a resourceUri
Added API for deleting a group i.e. telling each member to unsubscribe
all members of the deleted group
Updated baseUri retrieval
Merge remote-tracking branch 'github/Story5_jan' into Story5
Resolved merge conflicts