Combines different group additions into one plugin

• group multiple admin
• group activity (profile,dashboard,index,group widget)
  • can show more than one group activity
  • has support for river_comments and like
• group members widget (group only)
• group invitations widget (index, dashboard)
• group mail
• group invite
  • better error messages
  • free text with invite
  • listing of outstanding invitations
  • personal invitation revoke
  • add users to group
  • all users (admin option)
  • import users from csv
• group listing
  • alfabetical

As of version 2.3 of this plugin we offer the ability to set a group default access level (like with Site and User), this will however not work if you haven't applied Elgg/Elgg#253 to your Elgg installation.

This fix is in place for Elgg 1.9, so no modifications will be needed to the Elgg core files.