Group and User drop-down lists don't reflect the omero group permissions policy

[Rdornier]

When connected as a non-admin user, all groups and all members are by-default visible in the drop-down menus. I think it is worth to match the omero policy in that case :

• only display the groups the user is part of ==> for better visibility and navigation
• only display the members the user is allowed to see ==> for example, in private groups, they should be able to only see themselves in the drop-down, no other members.

The same logic could also be applied to the advanced search where by default, all groups and all members are visible in the drop-downs.

However, even if all groups/users are present in the drop-down list, the image access follows the right omero group policy and images, for which the connected user has not access, are not available. So, the 'backend' code works properly but the GUI does not reflect what is available for the current user.