Pie controls: Catching activation corner cases

As stated before there are still corner cases that may
deadlock pie controls.

This commit makes PieInputFilter respect ACTION_CANCEL,
simplifies monitoring mechanics in PieService and
fixes some corner cases in PieController that allowed that
activations got lost and thus pie controls got stuck.

Test case for PieController:
1) Enable pie controls
2) Enable top/bottom snap position for pie
2) Enable expanded desktop and check if it works
3) Disable expanded desktop
4) Lock your phone
5) Swipe from the top down/bottom up, as if you want to
   activate the pie from that position
6) Dismiss the notification tray and unlock your phone
   again
7) Enable extpanded desktop
8) Pie controls will no longer show up and
   "dumpsys pieservice" will show a active record.

Change-Id: Id9d2df6b2735a743eec2fd1ba809fd72be9474cc