Use dynamic static export feature of Next.js

[kylemh]

Feature request

@timneutkens reached out about the fact that our app is mostly static and that we can use an experimental feature to really speed things up 🚗💨

Proposed solution

Add the following to next.config.js

// Enable dynamic static exports (if a page can be static, it will be)
experimental: {
  autoExport: true,
},

Remove getInitialProps from _app.js

Move isLoggedIn logic of _app.js formerly within getInitialProps to be a part of componentDidMount(). Go off of client cookie instead of server.

More Context

Read at your leisure:
vercel/next.js#7293

[kylemh]

Closed in #592