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 
This is a bit tricky. See Jake's [blog post](http://jakearchibald.com/2014/using-serviceworker-today/) "in practice section".

To be safe, I think that we should rewrite this:
 - With a newly registered Service Worker in the activated state, try reloading the page to have it start controlling the page. You can also reload ...

And perhaps add the following note:
 - With a updated Service Worker in the installed state, try closing and re-opening the tab to have the newer Service Worker start controlling the page. Alternatively, use shift + reload followed by reload.

cc/ @jakearchibald