Redesigned alarm alert for 6AM usability.

* Snooze and Dismiss are now stacked vertically, which
  should make it easier to remember the order in which they
  appear if you don't have your glasses on and can't read
  them.

* The hit rectangle for Snooze now encompasses the top 75%
  of the alert, including the time, perfect for the wild
  flailing of the half-asleep user.

* Additionally, the larger Snooze means it's easier to hit
  (read: Dismiss is harder to accidentally hit) even if the
  display is rotated in a way you're not expecting (as in
  bug 1721234); just tap the middle of the dialog and you're
  safe.

* Finally, the dialog is now a stable width, so that changes
  in the time (displayed in a proportional font) don't cause
  the window to change size.

Bug: 1693158
Change-Id: I2d77f7267e2494f514ae15be32adbc3c8b586d5e