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.

PS2:  Cleaned up whitespaces, just because

Change-Id: I43b0b84217b7f9df1e5b230d2b376246df92648c