add jitsi microphone support

[mwfarb]

We can add some interesting interactions with remote users through builds that only work in Unity. Having spatial sound would help. Since we use a web library to use Jitsi one way to handle is a web shim attached to each local client Camera object. How to do this (in theory):

• write a jitsi shim js page to pass/feed mic/speaker
• add a web view to Object
• load js audio jitsi shim to web view
• pass jitsi token to jitsi shim
• does jitsi shim have access to mic/speaker through webview?

[mwfarb]

https://docs.unity3d.com/6000.0/Documentation/Manual/web-interacting-browser-js.html