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.

This change updates the frontend to use the built-in Sass support
provided by Create React App to simplify the development pipeline.

This change is one in a series of patches to remove the use of jQuery.
Here, we can utilize the scroll-padding CSS property to align anchors
properly in presence of a fixed top header.