When the user changes the periodic update checker preference update the alarm accordingly

ie. if we disable the preference and the pending intent exists then cancel the alarm, if we're enabling the preference and the pending intent doesn't exist create it and register the alarm.
Entering final testing for 2.0.3.a

In this alpha update I'm going to get rid of the announcements view temporarily since it's still under a lot of work and there's no real reason to have it available.