Use Next 13's app/ directory for pages

[keyserj]

Is your feature request related to a problem? Please describe. Next 13's app/ directory provides some nice features:

• font optimization (technically this works in pages/_app.tsx on the
  element, but we put the header outside of

  so it'd be awkward to apply the fonts on both)
• built-in metadata support
• cleaner page organization conventions (no need for .page.tsx!)
  • nested layouts
  • root layout replaces _app.tsx & _document.tsx
• server components

However, these things aren't being taken advantage of, mainly because Material UI and Emotion do not currently work smoothly with server components.

• Issue: emotion transform breaks with app root layout
• Issue: emotion support Next 13
• Issue: MUI example working with Next 13

We should take advantage of the Next 13 features when these issues are addressed.

Describe the solution you'd like

Describe alternatives you've considered

Additional context

Technical ideas