Refactor Encoder to Live Inside of Transport

Encoding is really a matter of the transport. The transport should bear full responsibility for what kind of encoding is used, if any. This will simplify and correctly place the responsibility of codec negotiation between the client and server in the transport as well, allowing specific messaging to be used for each encoder.

- For example, the `WebSocketTransport` can now alias encoder names/families as it makes sense for the web, and negotiate specifically with the corresponding client library (todo).
- For example, the `AndroidAoaTransport` will now be able to negotiate codecs in it's own special way that pertains to the Android system.

We need to think if there is still a common interface that can/should be expressed for encoders, even if they will soon live within the transports.