Update Tor to 0.2.4.21 and tor-browser to 3.6.1

This is an update to pull request #2557 which was merged and then removed with a forced push. This updates tor-browser to 3.6.1 and uses stable URL's for tor and tor-browser. The previous URLs would get deleted by the Tor project when new versions were released. These URL's now point to the Tor project archived files.