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. 
At the time I wrote this there was no way to attach a seperate CSS file to a specific tab. Now you can do it but only as of firefox 34. I am reluctant to use this API until we can mark 34 as the min version. Which is still a ways off I think.