Create demo in `static/examples` that allows sharing of screen w/ audio

[Ryan Olds]

Goal: Create a concise example that shares a screen/application w/ audio. Determine if it's possible to share audio without sharing a screen. Preferably we could share audio from a specific application.

Copy static/example/local.html and make a new example HTML file for sharing. Expand the new HTML file to support sharing a screen and audio.

Examples of screen and audio sharing:

• https://www.webrtc-experiment.com/demos/screen-and-video-from-single-peer.html
• https://stackoverflow.com/questions/19382444/is-it-possible-broadcast-audio-with-screensharing-with-webrtc