Introducing the CSP Fixer

@devoncarew

Devon: sorry, a couple of unrelated trivial changes have crept in.

I should also add tests.

Also note that I deliberately exposed the feature only in the form of an explicit action. I didn't want to build it into the Bower install/update sequence or anything like that because it's too early and too risky.

btw, you can use [parseFragment](http://www.dartdocs.org/documentation/html5lib/0.12.0/index.html#html5lib/parser#id_parseFragment) to have something parse in a different context. That's more or less how innerHTML works.