v3.5.7-beta

Critical bugfix release:

• rdflib-jsonld has been tombstoned. The latest version 0.6.2 removes all functionality. The developers recommend to use 0.5.0, but it cannot be installed with setuptools >= 58. Luckily, version 0.6.1 is still functional and compatible with setuptools >= 58, so this is the version required now by OSP-core.
• websockets 10 has been released, introducing breaking changes and dropping support for Python 3.6. Thus, for now the requirement websockets < 10 is enforced.