Feature/issue 165

Adds functionality that allows the user to whitelist certain potential trackers which need to be whitelisted to work. E.G. Youtube comments. This feature is already present in the chrome version but this would add it to the firefox version. CC @jsha for review. 
Oh, I get it now. Yes, good call. I just made a similar change in HTTPS Everywhere to not log about requests without a window. And it looks like we fail closed on such requests, so that's good.