SystemUI: Avoid "phantom" status bar collapsing

There is one specific case where the status bar may collapse
for no aparent reason: When the last notification is removed.

If Quick Settings panel is showing while such a notification
is removed, the status bar WILL collapse -- and the user may
be left wondering why, because the notification that was just
removed isn't visible in that case.

A way to reproduce this behaviour follows:
  1) Settings -> System -> Quick Settings Panel -> uncheck
     "Auto close panel"
  2) Dismiss all notifications, even the sticky ones.
  3) Open the Quick Settings Panel and tap the apropriate
     tile to light the Torch
  4) Tap the tile again, to extinguish the Torch.

As you can see, the Quick Settings Panel collapses. This
happens because Torch puts up a notification, when lit and
removes it, just after it's turned off.

This will happen to whatever notification that hides itself,
e.g. a GMail notification, which vanishes when you read the
e-mail on another device. This too will trigger this issue.

-----

This patch prevents the bar from collapsing, as consequence
of removing the last notification, when Quick Settings is
showing.

Change-Id: I8c7c015c836810a465268b25b90c9166c4485a9f
frameworks: Smooth background gradient

Credit to UBER for the images

Change-Id: I3655e9917610348100fa6cb5cede66a63ca82538
PIE: clear all button

Change-Id: I6333521999d846a417a0f8a3bba62a72aa876dbd
PIE: header with time and date (+///) for both panels

Change-Id: I400a88ff40b075bd1054ac123efca2b4a087fa73
PIE: /// is ready for prime time

Change-Id: Ib494c229fc65c99daadf598e3e29003950d55e72
PIE: one finger swipe-up for notifications

Change-Id: Ie23bd852fc41827f0067202685e7a97c595c3ac8