Bug 1047143 - close aps entering task-manager, exitToApp to open/restore

* 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 #23332 from sfoster/close-apps-task-manager-bug-1047143

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