Updating paging animation to spec.

- To handle the specific animation spec, we just animate the views
  manually instead of animating the stack scroll (like how we do when
  swiping to dismiss)
- Fixing a regression in settings the initial focused index when
  alt-tabbing
- Minor tweak to make the front most task smaller when in the initial
  non-paging mode

Change-Id: Ic5fd54500fd8ce8284c7aaeddb102b2291bcecac

Signed-off-by: Winson <winsonc@google.com>