HOVER: Implement hide only on swipe up

This commit was Re-committed by @namja in Triangles

* Add an Y axis HideHelper, just extend current X axis SwipeHelper and
  change interested methods behaviors
* Some clean up and indenting

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: I42a260ea993c614b0b9b4558a95dd44dd517c4f1

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/notification/HoverLayout.java