Add privileged and certified apps to webidl checker.

This adds privileged and certified apps to the webidl checker and reorganizes the result comparison code to reduce duplication.

I used Malini's marionette code to install the privileged and certified apps, but left the existing installation path for the web app, as that was used to save request header information into the results file. I split the javascript in the test app index.html to a separate .js file as that is required to run as privileged or certified.