Get information about HS from within browser

With hellais we started writing a patch for torbutton that uses legacy/trac#3521 (moved) to fetch info about the Hidden Services we visit.

A first implementation can be found in branch feature/hiddenservice_information at https://github.com/hellais/torbutton.git.

It currently just spits out the descriptor, but in the future we will want it to parse the descriptor fields, decode the intro points, and display all the useful information.