SIGNUP-246 Improve wording and positioning of notification / email options

    1. Switch 'Send Notification' with 'Announce Availability'.
    2. Change 'Send Notifications' to 'Notification of participant actions:' to make life that bit more clear.
    3. Introduce a field description to distinguish between creating and modifying a meeting.



git-svn-id: https://source.sakaiproject.org/svn/signup/trunk@307329 66ffb92e-73f9-0310-93c1-f5514f145a0a