Update handling of test configuration

[simleo]

This PR updates the handling of test configuration files (the params.jsonld files in the RO-Crate examples) in several ways:

• The format now allows for defining multiple tests
• Library code has been added to:
  • Parse the params.jsonld file into Test Python objects
  • Convert a collection of Test objects to a Planemo test suite description

The check_* scripts have been modified to use the above code.