1264 group bugs fixes

[sebgrebe]

• Shows internal users as organisers on group page if user is logged in. It previously did not show internal users as organisers in any case

• Fixes bugs with displaying membership and organisership on group page:

  • If a group is not public, on the group organiser's profiles page the group is not shown. It previously showed also non-public groups.

  • Shows the groups a user is organising, rather than a member of, under heading "Organiser". It previously showed who they are a member of

• Some refactoring of group test helper code

Closes #1264