Change SocksToRtc to have a freedom-compatible interface.

This change also adds a manifest.json for SocksToRtc, but this
manifest is not yet used anywhere or verified by the build.
This doesn't sound right to me. Can you explain? It's really easy to get these types wrong and the old type did previously catch a bunch of errors. I don't see what the problem with giving this the right type is... ?