Notifications are now light-on-dark in the windowshade.

Finally.

This also fixes that little 1px gap that would occasionally
show through to the carbon fiber background (changed to
steel cord for now) between the last notification and the
windowshade's handlebar. It still gaps a little while you're
dragging, due to the asynchronous motion of the various
windows involved, but when the panel is still you shouldn't
see any background. (Man, that drove me crazy.)

Bug: 2949229

Change-Id: If085f4ab7dfb7c3868c30469661907d5d63f070b