Dotcase: Improve handling of notifications

Handle and draw notifications in the order they are returned by the
INotificationManager (i.e., the order they were posted). This new
handling is also easier to extend with new apps (for existing sprites)
and new sprites altogether.

Also, if there are more than 6 notifications to draw, only draw the
first 5 and add a "..." sprite at the end. Now that we have a way to
handle more than 6 notifications, we can add more types of
notifications.

PS2: Use a Map instead of a bunch of Sets to map package names to
notification types

Change-Id: I4eba49420fb56028610a306585a977462c6f4113