Added watch.ino basic watchface sketch

Added watch.ino, an example sketch that displays a 12 hour clock to demo
low-power stop mode functionality.

Goes to sleep after 30 seconds of inactivity (not plugged into USB, no
touch activity) and wakes up (reboots) if the power button is pressed or
it is plugged into USB.

The current time is retained during sleep, but there's currently no
interface to set the time (It's always defaulted to midnight)