Add `generic json reader`

[Noordsestern]

Closes #98

This PR adds a simple json-reader creating test data from any JSON file.

The use case is data provided by APIs that is structured and well formatted. For using it with the original json-reader someone would have to put it in the Test Case Name - Tags - Arguments format which is complicated to automate. For working with not-explicit test data, the generic json reader is more flexible.