Demo updates

I've now updated all the non-apprtc WebRTC demos:
- tweaked HTML, CSS and JavaScript to validate with HTMLHint, CSSLint and JSHint 
- updated remaining demos to the new UI (though haven't done this for the face and desktopcapture demos)
- fixed various other minor wording and code formatting glitches.

@juberti @andresusanopinto @marwahvikas PTAL – but check my email first.
Agree. 

I'm also wondering if we should include boilerplate code programmatically, without repeating it in every file. HTML Imports are [well supported](http://caniuse.com/#search=html%20import) by the browsers we're targetting, and polyfills are available.

Aware that there are arguments pro and con.