Private group chooser 10104 develop

See ticket https://trac.openmicroscopy.org.uk/ome/ticket/10104
For a private group, don't show the "All Members" option in the group/user drop-down menu unless you are an Admin or Group Owner.

Also fixes the right arrows > on the groups in group/user menu.

To test:
 - login as regular user - Private groups will only show yourself in group/user menu - no "All Members" option.
 - login as root / group owner - As before, "All Members" option is still available.
 - All groups should have > arrow in groups/user menu.