DeskClock: Moar Timers!

* Instead of using a ViewPager with fragments for each Timer,
  switch to using a Recyclerview
* We can fit more than one Timer on the screen that way
* Account for portrait and landscape by switching the scrolling direction
* Account for tablets by showing 2 (portrait) or 3 (landscape)
  timers next to each other before starting a new row

Change-Id: If8ee65d650e085e1ae99d55c9956768e178091af