Two hours before a natural occurrence (AOSP DeskClock's lead), a silent
"Upcoming alarm" notification offers Dismiss, and the alarm's row shows
the same Dismiss as a chip. Dismissing is dismissUpcoming's own branches:
a repeating alarm skips that occurrence, a one-shot is switched off.
The notices are synced at the end of every reschedule, after the real
registration, and a third AlarmManager slot on its own request code
wakes when the next window opens. The sync is wrapped so a notification
failure can never stop a ring. Dismiss names the occurrence and is
refused once the alarm is ringing or has moved, so it can't get round
the dismiss challenge. No challenge is asked before the ring, as in
Google Clock.
Fixes#16
makiolaj
e43339c386