This change updates the web frontend to use Next.js instead of Create
React App (CRA). Next.js enables the possibility of rendering pages on
the server side (which reduces the time to first frame) and overall
provides a better development experience.

Future commits will try to futher optimize the implementation for
Next.js.

This change updates the frontend codebase by moving the component
styling into CSS module files as opposed to the global styles which we
used before. In addition, I have changed the syntax to the newer SCSS
syntax, which is more similar to CSS.

These changes reduces the styling conflicts that can occur between
components and allows us to migrate to systems that do not support
importing global styles in components. Moreover, we can benefit from
treeshaking using CSS modules.

This change updates the React dependencies to version 17, in order to
keep up to date with React.

This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.