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/views/edit.rb

@@ -18,6 +18,10 @@ module Precious
       def page_name
         @name
       end
+      
+      def mathjax
+        @mathjax
+      end
 
       def header
         if @header.nil?