Update clear all animation

- Fade out clear all button on tap
- Fade out silent label once there are no silent notifs
- Fade out footer once there are no notifs
- Round corners of dismissing notifs
- Pause to show "no notifications" before closing shade

Timing
- Remove wait before clear all swipe animations start
- Wait less between individual swipe animations
- Faster swipe animation

Bug: 172065269
Test: clear all with scroll, silent notifs, no ongoing notifs
	=> clear button fades out on tap
	=> clearable notifs swipe out with new delay, timing
	=> silent header fades
	=> no scroll change
	=> show "no notifications" at top of shade
	=> close shade
Test: clear all with no scroll, ongoing silent notifs
        => clearable silent notifs swipe out
	=> ongoing silent notifs stay
	=> silent header "x" fades
	=> show "no notifications" at top of shade
	=> close shade
Test: clear a lot of notifications
	=> pause same amount of time after swipe animations
	before closing shade
Test: press "x" to clear silent notifications
	=> silent notifications animate away
	=> shade stays open if there are other clearable notifs

Change-Id: I4db85068f46b95a34e71abb6428d3c2ae757cf0a