Basic Registration Sample

@jakearchibald @KenjiBaheux

The first of the micro-samples, which will likely be linked to from [Know Your Service Worker](https://jeffposnick.github.io/know-your-service-worker/cookbook.html) but are being kept in this repo for consistency with the overall samples strategy.

Other micro-samples to follow, roughly following what's outlined in [this list](https://jeffposnick.github.io/know-your-service-worker/cookbook.html).

You can view a live version of these changes at https://rawgit.com/jeffposnick/samples/sw-registration-basic/service-worker/registration/index.html