NotificationPanelView:   utilize observer for all system settings it cares about, and minimize work per specific onChange call

we already have a settings observer in place for quick pulldown so lets attach these getInts here instead of looking them up constantly

ps2: override the onChange(boolean, Uri) as opposed to onChange(boolean) observer method
     minimize the number of drawable updates by:
         when pulldown changes, just update pulldown variable
         when alpha changes, update port+land
         when port changes update port
         when land changes update land

Change-Id: I12a4914771e25f836e7c931a584eb046ff9409c9