Keep a mirror of the system icons while expanding the panel

Because the icons are shown in two different places at the same time
(in the QS header and the status bar), we introduce a mirror view
which does nothing except draw the contents of the other view to
draw it at both locations during the animation.

Bug: 15407838
Change-Id: I82edc8b4fb7347fa8dadfb81762d22796d37fa3c