Travis

This adds some minor travis support to the salt states, by setting up salt and deploying the salt states to a travis box. I made a [little post about using travis for salt states](http://blog.fict.io/automation/travis/travis%20ci/configuration%20management/continuous%20integration/salt/chef/saltstack/salt%20stack/2014/01/29/travis-for-salt-states/), as I haven't seen anyone else doing this yet. Some things that will need to change in a later PR.

* Actual checking of the validation step (salt will return 0 when running show_highstate even if it failed, because it thinks that it **successfully performed work on the minion** rather than **this was successful on each and every minion**.
* Verification that nbviewer fully deployed and works
* Setup GitHub triggers to fire builds off when either ipython/nbviewer or ipython/salt-states-nbviewer changes

I also handled empty pillar entries better (for the sake of travis).