Create Browser UI indication for current circuit status and exit IP

As we try to transition away from Vidalia (#6009 (moved)), one feature I expect people will miss is the Network Map. This will be hard to integrate with the browser in a way that normal people will understand, and initially the most expedient way to provide it will be through a separate download of Vidalia.

However, according to http://petsymposium.org/2012/papers/hotpets12-1-usability.pdf, unpredictable browsing delay is a major usability issue. The best way to solve this would be to provide some kind of circuit progress information in the browser toolbar, and provide a way to see your current circuit and current exit IP for that tab.

This is technically impossible for us to do until we have SOCKS username+password support (see #5752 (moved) and child tickets), but once we have that, we should implement this notification.