This change is a rewrite of the existing OpenDC frontend in order to
migrate to the PatternFly 4 design framework.

PatternFly is used by Red Hat for various computing related services such
as OpenShift, Red Hat Virtualization and Cockpit. Since their design
requirements are very similar to those of OpenDC (modeling computing
services), migrating to PatternFly 4 allows us to re-use design choices
from these services.

See https://www.patternfly.org/v4/ for more information about
PatternFly.

This change updates the frontend to use the FontAwesome 5 React library
that renders SVG icons as opposed to CSS icon fonts. This migration
resolves a couple of issues we had with server-side rendering of the
previous FontAwesome icons.

This change updates the frontend codebase to move away from the Google
login and instead use Auth0 as generic Identity Provider. This allows
users to login with other accounts as well.

Since Auth0 has a free tier, users can experiment themselves with OpenDC
locally without having to pay for the login functionality. The code has
been written so that we should be able to migrate away from Auth0 once
it is not a suitable Identity Provider for OpenDC anymore.

This change updates the structure of the OpenDC frontend in order to
improve the maintainability of the frontend.

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 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.