Package assets (#1493)

* Package static assets
* Fixed cancel button in editor
* Fix rake compilation task
* Add asset path helper
* Serve MathJax statically
* Fix mathjax in preview

lib/gollum/templates/layout.mustache

@@ -38,28 +38,21 @@
   {{#sprockets_javascript_tag}}editor{{/sprockets_javascript_tag}}
   {{/has_editor}}
   {{#mathjax}}
-  {{^mathjax_config}}
   <script type="text/javascript">
-  window.MathJax = {
-    tex2jax: {
-      inlineMath:  [ ['$','$'], ['\\(','\\)'] ],
-      displayMath: [ ['$$','$$'], ['\\[','\\]'] ],
-      processEscapes: true
-    },
-    TeX: { extensions: ["autoload-all.js"] }
-  };
+    window.MathJax = {
+      tex2jax: {
+        inlineMath:  [ ['$','$'], ['\\(','\\)'] ],
+        displayMath: [ ['$$','$$'], ['\\[','\\]'] ],
+        processEscapes: true
+      },
+      TeX: { extensions: ["autoload-all.js"] }
+    };
   </script>
-  {{/mathjax_config}}
   {{#mathjax_config}}
   <script type="text/javascript" src="{{base_url}}/{{mathjax_config}}"></script>
   {{/mathjax_config}}
-  <script>(function(d,j){
-  j = d.createElement('script');
-  j.src =
-      '{{base_url}}/javascript/MathJax-2.7.5/MathJax.js?config=TeX-AMS-MML_HTMLorMML';
-  (d.head || d.getElementsByTagName('head')[0]).appendChild(j);
-  }(document));
-  </script>{{/mathjax}}
+  <script defer src="{{base_path}}/gollum/assets/mathjax/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+  {{/mathjax}}
   {{#js}}<script type="text/javascript" src="{{custom_path}}/custom.js"></script>{{/js}}
 
   <title>{{title}}</title>