shake phone to reset sleep timer

I've implemented a new feature where you can shake the phone to reset the sleep timer. When there is 10s left of the sleep timer the phone will vibrate. If you sake the phone it will add 15min to the timer. It's nice when you are almost a sleep and don't want the screen light in your eyes.

It's a quick and dirty implementation but it works for my use, pull if you find it use full :)