New NotificationListenerService.

This is the best and only way for apps to listen for
notifications: create a NotificationListenerService, wait
for the NoMan to bind to you (as a result of the user
checking a box somewhere in Settings and agreeing to a
scary dialog box), and you'll start receiving notification
posted and dismissed callbacks. Your service, while enabled,
will also be able to clear one or all notifications.

Use this power wisely.

This change moves StatusBarNotification out of
com.android.internal into android.service.notification.
[Internal customers, including System UI and early users of
the system-only listener binder API, will need to be
updated.]

Bug: 8199624
Change-Id: I1be46f823d4b3ddc901109ec1e085cd6deb740c2