Feature add version to send

- This ensures that all messages outgoing have a 'v' for version in them.
The only such point is [here](https://github.com/OpenBazaar/OpenBazaar/blob/develop/node/connection.py#L59). It is inside `PeerConnection`, which is nowhere instantiated. Are we supposed to be calling `PeerConnection.send_raw` somewhere else? The only other such use was in `node/transport.py` and was [deleted](https://github.com/OpenBazaar/OpenBazaar/pull/828/files#diff-50cb406e13a62370336dc205e4d6452bL630) during the cleanup in #828.