Create descriptions for new Torbutton Security Prefs
We simplified our Torbutton Security Prefs in #3100 (closed), but Nick pointed out that we should probably have inline descriptions of each pref and why you would want to set them. I think this is a good idea, but I suspect that it will take a fair amount of time to both get the wording right and get the layout right, so I decided to push it out until we're more sure we actually have this time to spare before FF17 drops, or in case we simply decide we have to do it afterwords.