This adds WebRTC support to the realtime API and converts the Talk page to use realtime WebRTC. This has a huge impact on the existing realtime API and requires the inclusion of large libraries like Pion.

The Opus codec is needed for WebRTC and requires libopus. To keep this separate from the main Go executable and avoid requiring a C toolchain, Opus has been given its own backend.

TODO:

• Handle barge-in from the client speaker
• Prevent sending back multiple audio streams at once (assuming that is the problem)
• Replaced buggy Opus-go with libopus using purego binding to avoid CGO.
• convert to new UI (rebase on master)