Better Tor integration

[LachlanGunn]

Right now we depend on an external Tor to be up and running, but this isn't really ideal---we would like to ensure that it is configured properly, and on Windows it is necessary to distribute it alongside anyway.

What we should do, then, is write our own Tor configuration file, then add some code to run it directly and talk to the controller so that we can discover the port and have it automatically stop if we crash.