Calendar: Allow sharing of calendar events through an ics file

iCal specification rescources:
	http://build.mnode.org/projects/ical4j/apidocs/index.html
	http://www.kanzaki.com/docs/ical/

iCal validators:
	http://icalvalid.cloudapp.net
	http://severinghaus.org/projects/icv/

Change-Id: I87b12fd37aa7e3ad29bea79d4dbb152f868ff4f8
(cherry picked from commit a4c6896)