Implement Outputs Rulset

[EttoreM]

This PR addresses #35

First commit containing only some rules coded in SHACL and the corresponding python tests.

[EttoreM]

@elichad

I think the only opened issue left is that of the values of expected_triggered_requirements and expected_triggered_issues.
Whatever I put there for testing the two SHACL constrains left, the tests fail.

[elichad]

Thanks @EttoreM !