This change removes the OpenDC Harness modules from the main repository.
We have made the decision to take a different direction regarding the
specification and execution of experiments. The design of the current
harness does not integrate well with the specification of experiments in
the web interface. The new version focuses on proper integration with
the web interface, as well as via the command line interface.

This change upgrades the Gradle build system to version 7.1.

This change updates the Gradle build configuration so that the
application modules (as opposed the libraries) are not published onto
Maven Central.

This change updates the Gradle configuration to include experiments in
the main distribution of OpenDC. Users can directly execute the
experiments from the command-line without having to recompile the entire
code-base.

This change splits the OpenDC Experiment Harness into separate modules.
This prevents users from pulling in unnecessary dependencies when
depending on the harness API.

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.