Add number of notifactions indicator to app and folder icons.

This makes use of the new NotificationListenerService introduced in API 18.
When enabled an indicator showing the # of notifications an app has will
be displayed in the upper left corner of the icon.
Folders will show the total of all notifications for apps inside that folder.

PS2:
Change commit title

PS3:
Start NotificationListener in onResume instead of onCreate.

PS4:
Add mapping of com.android.phone to com.android.dialer

PS5:
Remove debug logging

PS6:
Hide notifcation count when calling super.dispatchDraw() and then
draw the notification count indicator on top of everything else
using drawChild().

PS7:
Fix ClassCastException

Change-Id: I29e5041ab996fe413744be8d022a37961b4d244f