Add support for aiida-core==2.X

[mpougin]

Update the codebase to support aiida-core v2.X, mostly via:

1. Adding core. prefix to entry points.
2. Removing dict=/list= keyword arguments in the corresponding constructors.
3. Use new base name spacing.

Since the CI was failing in many ways, this has been tweaked and fixed as well:

1. Updates to the pre-commit, switching to the black formatter, using isort and updating pylint.
2. Adapting the Docker build for running the examples to:

• use the 2.3.1 version of the aiida-core image.
• Update RASPA to v2.0.47
• Include the run_examples.sh file, where we select the examples to run for the CI.

3. The CI tests are now split in the actual pytest tests, and examples. Running the examples via pytest seemed quite broken, and this way we can split the two so we can e.g. only run the examples for release PRs.

The repository was also cleaned up of several files that no longer served any purpose.