GStreamer WebRTC single direction demo

Fork from: https://github.com/centricular/gstwebrtc-demos

The original demo(s) is a bit complex for me, so, I simplify the original bi-direction demo to single direction, which could transform video from any headless device (e.g. Raspberry Pi) to remote web browser.

Usage:

1. Start http server to serve folder web-page/, could simply by busybox:
   cd gst-to-browser/web-page/ && busybox httpd -h . -f -p 8000 -v
2. Start signal server:
   cd gst-to-browser/ && ./signal-server.py
3. Start up camera side program:
   cd gst-to-browser/gst/ && ./gst-no-ssl.py --ws-url ws://IP-OF-SIGNAL-SERVER:8443/gst
   (use ws://localhost:8443/gst by default if no --ws-url argument.)
4. Open your web browser to visit url http://IP-OF-HTTP-SERVER:8000
   (the ip address of http server is the same as signal server by default.)