workspacesView: Add some more spacing between window and workspace thumbs

https://bugzilla.gnome.org/show_bug.cgi?id=582650

data/theme/gnome-shell.css

@@ -569,7 +569,7 @@ StScrollBar StButton#vhandle:active {
 /* Overview */
 
 #overview {
-    spacing: 12px;
+    spacing: 40px;
 }
 
 .window-caption {

js/ui/workspacesView.js

@@ -864,6 +864,7 @@ const WorkspacesDisplay = new Lang.Class({
         let clipY = y + (fullHeight - clipHeight) / 2;
 
         let widthAdjust = this._zoomOut ? controlsNatural : controlsVisible;
+        widthAdjust += Main.overview._spacing;
         width -= widthAdjust;
         if (rtl)
             x += widthAdjust;