Process RSVP Intent Without Event Editor

When processing an RSVP Intent
(https://www.google.com/calendar/event?action=RESPOND) there's no need to open
the event. Simpy update the RSVP directly from the intent handler.

Change-Id: I66c8c533b8babe64aa4083dc998b497c04ded2c9
(cherry picked from commit 296ea5d)