Disable peeking at individual notifications.

Now tapping anywhere on the notification/clock/status end of
the system bar will bring up the notification panel.
Swiping up anywhere in that region works as well.

This change also adds visual touch feedback to the panel
trigger area.

Bug: 4723688
Change-Id: I5e24fea1231b798c41ddd48c0c42c283c92ebe65