Send meeting invitations for new/updated Exchange events

* Wrote utility to create an ics file (iCalendar) based on a
  CalendarProvider Event.  This is a good first pass, but we need
  to consider whether to include alarms, etc.
* Use aforementioned utility and new convenience method to send
  meeting invitations to attendees of newly created meetings (events)
  when they are uploaded to the server via the CalendarSyncAdapter
* Overall, attempted to modify existing provider and rfc822 output
  code as little as possible.  Rfc822Output is actually very limited
  in its capabilities and should be made more robust in future

Change-Id: Ie20b9137df56dc414de6737d05fa40ec9cdf47e0
5 files changed