Feature: Bedtime calculator

Adds a bedtime calculator to each alarm. The calculator works by
counting backwards in sleep cyles (90 minutes), then calculating the
times you'd need to go to sleep in order to wake up in between them. It
can help you wake up feeling less groggy. The calculator displays four
suggested sleep times ranging from 4.5-9 hours of sleep.

Change-Id: I7ad932da7955d8f058392562ffc85c9af0f5206f

Conflicts:
	res/values/cm_strings.xml
	src/com/android/deskclock/AlarmClock.java