Add ability to set media bit rate in rtc client

We are finding that we need to adjust the media bit rate in Chrome (b=AS:?).
http://www.rtcbits.com/2016/11/controlling-bandwidth-usage-in-webrtc.html
I've embedded the ability in the connect-rtc.js file.
https://webrtchacks.com/limit-webrtc-bandwidth-sdp/

I would prefer if the original project has this facility so that it can be called and set from an external client.

Start by reading connect-rtc.js and the linked WebRTC bandwidth references to understand how media bitrate is currently adjusted. Determine the external-client API and bitrate behavior required, then verify that a caller can set the bitrate through the RTC client and that the resulting SDP or media configuration reflects it.

Written by the indexing model from the issue text.