deploy a demo instance of collective.cover to Heroku

After this is merged, it would be really cool if you guys add more stuff to testfixture profiles so that that the demo instance already has some valid content that visitors can play with. Or create a demofixture with this content.

And find me on IRC at some point so we configure Travis to automatically deploy the latest code to Heroku on successful builds. 
Nope, buildout fails without it.