Use ParceledListSlice to send the list of active notifications
from NoMan to NotificationListeners.
This allows us to simplify the API to what it was before
introducing the "String[] key" workaround for dealing with large
numbers of StatusBarNotifications.
While we're at it, rename Ranking.getIndexOfKey to something that
makes more sense.
Bug: 15126927
Change-Id: I02c2087978c6c4ec1198be496c6250a66143ecb3