Added passing the contextCreated parameter to aid mollom perform checks ...

...on comments posted to older/newer content.

Discussed this yesterday over lunch with @blackskad (https://twitter.com/blackskad): How about passing the created date of a blogpost as extra context to Mollom? We could assume that comments on older content are more probable to be spam.

Apparently, there's an - yet to be documented - contextCreated parameter in the /content API call. 

https://twitter.com/blackskad/status/482495776913129472 (Dutch)

I'm going to add this to my own blog so things can be tested on the server side. 
Although experimental, I'll add it as a PR for later inclusion.