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 moves the OpenDC modules previously living in the simulator/opendc
directory to the simulator directory itself given that we do not make a
distinction between OpenDC and odcsim anymore.

This change updates the Dockerfile for the simulator to reduce its size.
By using Docker stages, we can split the build image from the runtime
image that only contains the runtime binaries.

This change adds support for processing the experimental results by
means of a Spark data processing pipeline.

This change re-adds the simulator service for the docker-compose
configuration, such that it will listen for incoming jobs from the API.