Consider adding demo renderer to codebase

[davemevans]

The renderer demo at http://sandflow.com/imsc1proc/index.html has proved really useful for debugging and determining if issues lie in the library or the integration elsewhere, but obviously it can only use the version of the library hosted alongside it.

It would be awesome if this app could be added to the src/test/webapp so that versions of the library built locally can be tested in the same way.

[palemieux]

Master branch at https://github.com/Dash-Industry-Forum/dash.js implements imscJS