[Nexus] Renegotiate TODO

[ddbnl]

The nexus app has helped me a lot with understanding WebRTC, but I've gotten stuck at adding a new track to an existing connection (goal is to share camera and screen at the same time). Tracing through the code I found that there is a "TODO: renegotiate" line in the following file, which I believe could help me if implemented.

I've tried to implement it myself with no luck as a beginner to WebRTC; would it be possible to fill in this function, or give a clue regarding how to go about implementing it? I don't mind making a PR if I manage to fix it with some hints :)

Thanks for the great example app.