Add Sitelinks Search box.

This pull request adds a search box in google that will search in the search module. (sounds a little meta).

Docs can be found here, and will be a little clearer then my explanation:
https://developers.google.com/webmasters/richsnippets/sitelinkssearch

Preview from the google documentation: 
![image](https://cloud.githubusercontent.com/assets/1398405/4754392/a1c79940-5abd-11e4-9064-e0a11dff8f76.png)