Extract QS animations to QSContainer

Move some of the logic for QS animations into QSContainer with a
stable interface for NotificationPanelView to call.

This also moves the QSPanel out of the scroll container and up
to live in with the header (QSContainer is the parent of both
the header and the QSPanel now).

Change-Id: I618e363ccca2be9197a4a75256e0b7841ca2c61c