Drop support for client-side negotiation features

Things like [this](https://github.com/websdk/nap/blob/6c009ab90a9e0e192cefa0f5835449ddf5d3ff37/src/nap.js#L10) should really be the concern of clients, not nap. We should drop support for it, or at least extract such features into some library to help implement web based clients.
