Align bar icons on a shared baseline

shell/Commons/Style.qml

@@ -343,6 +343,7 @@ QtObject {
     readonly property int sizeVertical:   root.barToken("size-vertical",   28)
     readonly property int iconSlot:       root.barToken("icon-slot",       27)
     readonly property int iconCanvas:     root.barToken("icon-canvas",     16)
+    readonly property int iconFont:       root.barToken("icon-font",       13)
   }
 
   function refresh() {