Fixed several bugs with the notification shade

Cleaned up the code around mMaxPanelHeight of the
PanelView which could lead to flickering during
peeking.
Changed the panel opening logic to account for lag
when we need to wait for a layout, which could lead
to inconsistent animations.
Fixed a bug where holes could appear in the shade
when notifications were updating.
This also improved the general updating behaviour
which is now done in a nicer animation.

Bug: 15942322
Bug: 15861506
Bug: 15168335
Change-Id: Ifd7ce51bea6b5e39c9b76fd0d766a7d2c42bf7a4