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
From Jake's blog post, we should call out the fact that ops here might delay the page load and resources. So, the idea is to do as much as possible during the oninstall phase where there isn't such issue.