* Add AMP First example

The sample demonstrates how to build an AMP First Site with AMP. If
follows all the best-practices recommended by Lighthouse and will
result in a fully-qualified PWA.

Live demo of the page: https://my-next-app.sebastianbenz.now.sh/#development=1

* small improvements to AmpScript and AmpState

* remove gitignore

* Update example

* Move styles down in Layout

* Apply lint fix and tweak prop-types

* Add warning for host header usage