Change overview animation to scale instead of translationX

As you swipe up to overview from home, workspace scales down and fades out as before,
and now recents scales down from 1.2f on top of it. The interpolators are set such
that the workspace animation is seen before the recents animation. Also, we don't
scale down all of recents, only the visible pages (current and adjacent).

Change-Id: I5f8bfe8cafeaa41d26873c63549735d7bdff2bce