DeskClock: Fix pending bugs

Fix some pending bugs from Stopwatch & Countdown:

- Add not translatable to arrays.xml
- Set fragment title size to 18sp (aosp default)
- Push over the add current timer text now adds the current timer, and not reset the timer
- Disallow create a new countdown timer if timer is 0
- Now, when "Lower times are better" is selected for the last lap behaviour, the green color
  is asigned for lower times.

Patch 2: Typos in arrays.xml
         Revert refreshRate patch because it didn't improve the lag when both timers
         are running. Change Digital Time Clock to decrease the redrawing times.
Patch 3: Change "swipe to right" text to "swipe to left", as Simon suggests
         Change layouts to make all buttons fit with the max height of them
         Fix a bug that cause to blink clock when the screen is rotated and the countdown
           is still running
         Protect DeskClockFrament#setWakeLock from NPE when FragmentActivity is null
Patch 4: Fix bug introduced in patch 3: the set button is not update the timer ui.
         Strings: Use unicode chars for copyright symbol
Patch 5: Fix a description and remove unnecessary lines at the bottom of strings.xml
Patch 6: Fix copyright signs, replace CountDown/Stopwatch with Countdown/Stopwatch in
         descriptions, remove useless comment, comply with Android Writing Style
Patch 7: Fix another copyright notice

Change-Id: Iabf564ab5a254f2f8b5d011ce6c08a271885ea1d