relay: Implement config for TorRelay

TorRelay is an empty place holder at the moment but the starting point of everything.

This ticket is to first implement a Config object (like TorClient). This will pave the way for #1449 KeyMgr that requires a configuration for the path of the keys.

And then, we can continue with a ChanMgr requiring the KeyMgr and other config options.

Essentially, this would be the starting point of for all our Lego blocks.