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

I am not sure we need to record initialPosition.
We should not keep two many different 'active app' info in different modules.

What I am thinking is:
* If an app is closed by 'entertaskmanager', we don't update the active app infomation in appWindowManager. (is this the change in app_window_manager you made?)
* If the user presses home button in taskManager we just call AppWindowManager.getActiveApp().open(); If AppWindowManager.getActiveApp() is null then we call homescreenLauncher.getHomescreen().ensure(true) then open();