This change updates the source structure of the OpenDC frontend to
follow the page structure.

This change updates the topology view in the OpenDC frontend to isolate
the world coordinate space. This means that zooming and panning should
not affect the coordinates in world space (but only in camera space). In
turn, this allows us to remove the dependency on Redux for the camera
controls.

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 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.