SystemUI: fix recents minimization animation

Splitting up the buttons into each class is cute,
but it only seemed to complicate its interactions.
The instantiation was wrong before anyways and
onTouchListener was never being registered
(which is why the animation was wonky).

Change-Id: I4194569aaf0099754852d5cfb83f308f3271008b
Signed-off-by: Roman Birg <romanbirg@gmail.com>