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 OpenDC frontend to use the normalizr library for
normalizing the user topology.

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

This change refactors the frontend to use hooks for obtaining state
within the Redux store as opposed to using Higher-Order Components
(HOCs). This eliminates a lot of clutter in the components.

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.