Thumbnail enter animations for multiwindow.

The multi-window differs from the full screen entrance animation by
using translation to make the window travel from the thumbnail to the
final position. It also takes into account the surface insets when
determining scaling animation. It doesn't use clipping at the moment,
but that would be a near future improvement.

Change-Id: I7f310850713448b820b9e94ac2f8fbf74563068c