Improve the robustness of authinstance-in-session handling, to handle an unduplicatable bug (at least by me).

All users who log in to the system should have a valid authinstance in their session. Apparently however, some don't. I can't narrow down how this happens, but this patch will make sure things don't blow up in this case.

Conflicts:

	htdocs/view/columns.php
	htdocs/view/layout.php

When assigning view access, allow users to assign access to any group, not just the ones they're in.

'Owner' is a hangover from the old group stuff anyway. It doesn't make sense to delete a group just because a group admin has been deleted.