SystemUI: Option to display Quick Settings when there are no ongoing notificaions

Added member function hasClearableNotifications to class
PhoneStatusBar. This function returns true when clearable
notifications are present on the status bar. Also, onTouchEvent in
NotificaionPanelView now flips to Quick Settings if there are no
ongoing notifications, and the QS_QUICK_PULLDOWN is set accordingly.

Change-Id: Ia77f90b19c7b408b7fc9376b6914e3173b734655