Bug 591246 - Move towards shell-black02 mockup

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.

js/ui/docDisplay.js

@@ -68,13 +68,13 @@ DocDisplayItem.prototype = {
 
     // Creates and returns a large preview icon, but only if this._docInfo is an image file
     // and we were able to generate a pixbuf from it successfully.
-    _createLargePreviewIcon : function(availableWidth, availableHeight) {
+    _createLargePreviewIcon : function() {
         if (this._docInfo.mimeType == null || this._docInfo.mimeType.indexOf("image/") != 0)
             return null;
 
         try {
             return Shell.TextureCache.get_default().load_uri_sync(Shell.TextureCachePolicy.NONE,
-                                                                  this._docInfo.uri, availableWidth, availableHeight);
+                                                                  this._docInfo.uri, -1, -1);
         } catch (e) {
             // An exception will be raised when the image format isn't know
             /* FIXME: http://bugzilla.gnome.org/show_bug.cgi?id=591480: should