PIE: Use case upgrade and bugfixes:

1.Play with navigation bar height instead of view state. Just set navbar height to 0, even because
  swipe gesture is disabled aswell so it will never be called. This way we handle just one var
  that is height. PhoneWindowManager will take care to calculate decors since it uses height (width
  in landscape) as a param in the calculation.
2.Remove dependency from last systemui flags. Right now before this patch, pie showed no matter if you
  were in forced or native immersive mode. That made us bring a couple of hacks to keep this marriage,
  but there is no need in the end cause PIE is an alternative way you have to enable. That means apps will (should)
  use their own immersive mode at first unless you have already PIE mode on. Not all apps hide navigation bar,
  that means they can not cover the entire screen height (portrait). That's why there is forced mode, to supply this
  cause force the app to go immersive. Last but more important, immersive API works again now :)
3.Cleanup some vars not used anymore, just need observing main immersive mode now.

Change-Id: Ia17bb7ede36d5a14c8508841e32910e6e9595310
Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>