#622: implemented (added AccessControlConfig)

[hohwille]

This PR implements #622:

• Provides a new class AccessControlConfig that implements AccessControlProvider. It can therefore be used as a drop-in replacement for access-control-schema.xml and AccessControlProviderImpl.
• Includes an example config and a JUnit test that verifies that all is working as expected.

Feedback to improve the config "API" is most welcome. I did not (yet) deprecate the code that may not be used anymore such as AccessControlProviderImpl and AccessControlSchema, etc. First I want to await feedback from others but I am quite convinced that the old XML stuff is kind of odd compared to the new approach. We still have issues with referencing and code-generation from the XML. All solved as a single source of truth with the new approach where everything is in one place.

[hohwille]

@maybeec thanks for your review feedback. I have updated and improved the test accordingly. Hopefully everything is fine now.