This commit contains various fixes and enhancements, mostly because I
was too lazy to commit small changes.

* Add topBarCollapseOnScroll style property which compliments
  navBarHideOnScroll. This property is needed when showing a
  collapsing topTabs screen. In this case the developer might to keep
  the titleBar bar when the screen is collapsed.
* Reduce collapse sensitivity by taking scaled touch slop into account
* Cancel touches when collapsing. This fix prevents buttons from
  responding to touch events when collapse ends.