Opentok

- OpenTok SDK now accepts Vonage credentials so it's possible to use the existing OpenTok SDK with the Vonage Video API
- Add additional headers to some requests
- Internal changes to the `Opentok.create_session` method

- Add new `max_bitrate` option for archives
- Change to create JWTs by default in the `Client.generate_token` method. T1 tokens can still be created by setting `use_jwt=False` when generating a token.

- Migrate from using `python-jose` with native-python cryptographic backend to the `pyjwt` package

- Fix a bug with SIP options in the `Opentok.dial` method

- Add `publisher_only` role that can be specified when generating a token.

- Fixed an issue with the `opentok.create_session` method