Organize files

[aganders3]

I mentioned this in a comment somewhere, but I just don't want it to get lost. When we have a break on features I think we should organize our files a bit more. I think it's fairly typical for React projects to have something like this for directories:

src/
  components/ (tsx modules)
    app.tsx
    main.tsx
    scene.tsx
  hooks/ (custom hooks)
    useSelectionBox.ts
  lib/ (non-React code)
    PointCanvas.ts
    ViewerState.ts
    ...