Remove the last use of passing width into Dash by having the
Pane with the previews scaling dynamically and relying on
Clutter scaling.
If we only have one workspace, don't display a selection frame
for it.
Rework Dash into a searchArea and sectionArea, which get
explicitly sized by overlay.js. We use the workspaces size
to choose the size of those dash areas.
Switch dash colors/boxes etc. to ones from shell-black02.
Add a gradient to the panel.
Add a magnifier.svg for use in search.
