Tune AlarmActivity tablet layout

Bug: 17438994

- Align snooze/dismiss button based on evenly spaced grid.
- Increase font size on tablets for "swipe..." message and alert text.
- Tighten clock spacing by disabling font padding (necessary for
  sw600dp-land).
- Increase "swipe..." padding from bottom.

Change-Id: I072a68284304cb9f15811c66f66282477e0facc9