Detailed Service Worker registration example.

@jakearchibald @KenjiBaheux

This sample takes things a step further by attempting to illustrate aspects of a Service Worker registration:
- Whether SW is available
- Whether the current page is already controlled by a SW
- Whether the current registration attempt represents the `installing`, `waiting`, or `active` SW
- The state transitions of the SW associated with the current registration

You can view a live demo at https://rawgit.com/jeffposnick/samples/sw-registration-events/service-worker/registration-events/index.html
@jeffposnick 
"Available" might be confusing, perhaps change it to:
 Available behind the experimental web platform features flag in Chrome 39+ (<a href="http://www.chromium.org/blink/serviceworker/getting-started">learn more</a>).