HTML report (code review only - do not merge!)

### Do not merge this pull request. It is for code review purposes only

This builds on the HTML report pull request submitted by @angelc04. It is dependent on changes that will be in the next release of Marionette. You can use Marionette from mozilla-central if you want to test this. I have uploaded an example report here: http://people.mozilla.com/~dhunt/gaiatest_results.html