SystemUI: Swipe to float for notifications and recents

Recents ScrollViews set separate trigger directions on
SwipeHelper (LEFT for vertical and DOWN for horizontal).
Directions are chosen as the opposite of the 'natural'
swipe-to-dismiss direction performed by the clear-all
button. onChildTriggered() will open the app in floating
window mode. To confirm this behavior for horizontal and
vertical recents views, separate settings confirmation
dialogs are shown with appropriate PA-style graphics (Gimp
sources on request).
- Swipe status bar notification for floating window:
Analogous to recents, here the NotificationRowLayout sets
the trigger direction to LEFT. It also got its own
confirmation dialog together with new hint graphics. After a
child is triggered, the app is started in floating window
mode by performing a click causing the notification to
disappear (exactly as it would anyway, if the app would have
been opened in 'normal' full-screen mode).