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. 
I think path.contains is overly generous here. You probably want something close to path.startsWith(name), but you might need to strip off http[s]:// from the beginning.