Leave and join groups

This is the 'cleaning up' of all the work I did whilst at Aptivate. It covers these cards:
https://aptivate.kanbantool.com/boards/5986#tasks-2139627
https://aptivate.kanbantool.com/boards/5986#tasks-2139623
https://aptivate.kanbantool.com/boards/5986#tasks-2139617