Add support for managing OnionBalance resources

[kragniz]

https://github.com/DonnchaC/onionbalance or something similar to add basic load balancing across multiple backend onion services.

[bugfest]

Hi @kragniz, just got it implemented in my fork: https://github.com/bugfest/tor-controller (since v0.4.0)