Bug 1047143 - close aps entering task-manager, exitToApp to open/restore. r=alive

* Fix assumption that home event means homescreen opens in SoundManager,
* Remove appwillopen handler in AttentionScreen, applaunch will suffice
* Also listen for search app's requestforeground event
Merge pull request #23384 from sfoster/bug-1047143-active-app

Bug 1047143 - close apps entering task-manager, exitToApp to open/restore. r=alive