add hbs helper to enable extending css js in advanced example

Changes: 
- add block, extend hbs helper util for advanced example to show the ability to extend/customize js/css for different handlebars

Screenshot of the output
![screen shot 2014-08-06 at 4 20 08 pm](https://cloud.githubusercontent.com/assets/1945035/3835517/cb9548e2-1dc0-11e4-824b-3e1944583fd7.jpg)