Switch to yajl for JSON
Visual Campaigns refactor

* Fetch multiple visual campaigns with a single API request
* Enqueue a VC instead of fetching it right away
* Add pushdown-global and pushdown-homepage nodes
* Cookie.set now accepts an object of attributes
Remove logging, fix adhost URL, check that cookie key isn't null
Merge pull request #199 from SCPR/adhost-multi-fetch

Adhost multi fetch