Initial site design

Here is the initial site layout. I have already updated some pages to match the new styles. There are still some things to be improved in the layout:

* Background image, the current one is of bad quality
* The top navigation on small screens
* The footer

The front page Mailchimp form has been removed to match the new design. The subscribe link in the top needs to open in a new blank page with the form provided by Mailchimp (which we can also style up with logo at least and similar colours).

I have not squashed commits so that you can track how each page layout has changed.