SAK-25958 Group Add and Edit page: Change default empty value in select list for joinable groups


git-svn-id: https://source.sakaiproject.org/svn/site-manage/trunk@307477 66ffb92e-73f9-0310-93c1-f5514f145a0a
SAK-25947 Add Option to unjoin from a joinable group


git-svn-id: https://source.sakaiproject.org/svn/site-manage/trunk@307480 66ffb92e-73f9-0310-93c1-f5514f145a0a