Create initial [robots.txt](http://www.robotstxt.org/robotstxt.html)

* Remove referer check for statics
* Leaving /images and /xml in for the moment in case SEO needs this for any reason... revisit when #249 is complete

Closes #391
Merge pull request #392 from Martii/Issue-391robotsdottxt

Create initial [robots.txt](http://www.robotstxt.org/robotstxt.html)

Auto-merge