Add Layer switcher tab to the key configuration popover. #22

The icons used in this commit are not final, as this is just a mockup,
and for this purpose it was easier to use fontawesome (as previously),
instead of adding the svgs.

script.js

@@ -232,6 +232,12 @@ $(function() {
         title: 'Keypress',
         content: 'keypress'
       },
+      {
+        type: 'default',
+        icon: 'fa-clone', // The icon for the tab will be a layer icon in svg. But for the mockup it was easier to just use something similar from fontawesome.
+        title: 'Layer',
+        content: 'layer'
+      },
       {
         type: 'default',
         icon: 'fa-mouse-pointer',