Suspend apps - disable notifications

Disable notifications and posts for suspended apps by
verifying if the package is suspended in NotificationManagerService
where AppOpsManager.OP_POST_NOTIFICATION is checked.

Note that the notificationEnabled user preference is
preserved when unsuspending.

In a following CL will make the "Block all" notifications
setting while an app is suspended (in Settings -> App Info)
readonly so that the user can not turn notifications on.

Bug: 22776761
Change-Id: Ie8edba508bd23406445f9a014404b6d3b17cb223