Server rendering to improve load time performance

[OliverJAsh]

Demo: https://simple-offline-blog.herokuapp.com/

For these users:

• First time users, who won't yet have the ServiceWorker installed;
• Users without ServiceWorker support;
• Users without JS (unlikely, but hey)

… rendering on the server will improve load times, because the content is in the very first request for the HTML. No further network requests nor JS execution needed.

I took the shared rendering approach for its nice developer ergonomics. Server renders the core content, client re-renders to enhance the content, all using the same template code.

Here is the updated architecture blob:

• Server renders content, client renders with enhanced content. Both renders
  share the same template (aka isomorphism or shared rendering).
• A ServiceWorker is installed on first visit. Subsequent navigation requests
  will be proxied by the ServiceWorker, which will respond with a cached shell
  (a wrapper for the content). The shell contains JavaScript which is
  responsible for fetching and rendering content.

Note that this means browsers without ServiceWorker support will just continue
to use server side rendering.

[OliverJAsh]

TODO: Use content negotiation