Groups users menu 12082

This addresses several issues with the Groups & Users menu in web.

To test:
 - Log in as a regular user (not Admin) and try switching user and group. Should work much as before, with slightly different layout.
 - Menu should remain open until you click a user or click outside of menu.
 - On Safari, shouldn't have a problem with vertical scrollbar when the Projects/Datasets/Images panel needs scrolling (fixes http://trac.openmicroscopy.org.uk/ome/ticket/12082)
 - Log in as Admin (with large number of groups).
 - When list is longer than the screen, dialog should expand almost to the bottom of the screen and then scroll to handle large lists.
 - You should see "My Groups" listed first, followed by "ALL Groups".

Test on tablet:
 - All the above functionality should now work on a tablet!