Support sharing calendar events as .vcs files to MMS.

- Export calendar events to a temporary .vcs file. Currently, the actual
  file format is still ical, this may need to be reformatted to actually
  contain only vCalendar content.
- Share this specifically to the com.android.mms package when the share button is clicked.
- Share the event as ical .ics to all other applications.

Change-Id: If337360b17d4071d580087ecc97a2397d0563ff6