New typeahead search for user entry when managing groups.

Will pull usernames both from the local authentication database and LDAP.
Configure the maximum number of results returned when searching each authentication source.
Added unit/integration/selenium tests for username completion
Tweak the styling of the add-member actions on the group edit form; Also patched the group.js to only add to the list if the dropdown isn't visible - so return selects from the typeahead, populates the input, subsequent return adds the user to the list;
Merge pull request #393 from hudmol/browse-users

Add a typeahead find when adding users to groups