Support addressing peers with onion tor addresses

It will be neat to automatically use local tor to communicate with other peers that are behind hidden services in tor network:
```
proxy: "127.0.0.1:9050"
externalAddress: "57qr3yd1nyntf5k.onion" # own onion address
nodeSeeds:
  - "57qr3yd1nyntf5k.onion" # other peer onion address
```

Reference implementation in BTC: https://github.com/bitcoin/bitcoin/blob/master/doc/tor.md