Adjusted the behavior when expanding the notification panel

The topmost notification is now not collapsed anymore but slides in
expanded from the top. Therefore it's layout doesn't need to animate
anymore. This also cleans up a lot of code in the algorithm which was
depending on this resizing which isn't needed anymore.
In order to have that transition working perfectly, the padding when
collapsing a card is now the same as the slowdown length.
Also improved the logic when notification contents are allowed to
animate and when not.
Also fixed a bug where the top notification was cut off when QS was
expanded.

Bug: 27402534
Bug: 18434284
Change-Id: I31afa199d38d94e74fd45500c2236ffdb51d989d