Added StyleGuideUrl to top panel.

layouts/partials/toolbar.hbs

@@ -9,6 +9,9 @@
   </div>
 
   <div class="page_toolbar__right">
-    <a href="{{ previewFrameUrl }}" target="_blank" class="open_in_new_tab"></a>
+    {{#if config.styleGuideUrl}}
+      <a href="{{ config.styleGuideUrl }}" target="_blank" class="palette" title="Open Style Guide"></a>
+    {{/if}}
+    <a href="{{ previewFrameUrl }}" target="_blank" class="open_in_new_tab" title="Open in New Window"></a>
   </div>
 </header>