A new clock widget to create lock screen appwidgets

This new widget replaces DigitalClock. It listens to all the correct
system events and offer the ability to customize the formatting
patterns in 12-hour and 24-hour modes. It also supports fixed
time zones to create world clocks.

One more step towards becoming ClockOS!

Change-Id: I677e5dfca8cd8c8d1f8c49e54d7507f4d1885bf4