Introduce mocked TRIAS service for testing

[andaryjo]

The module testing currently tests the functionality of the module for multile TRIAS providers to ensure it's comaptibility. However, I do not think that this is a good testing approach as it depends on the availability and correct implementation of external providers.

Instead, testing should be done on a mocked implementation of a TRIAS provider (maybe by generating random XML responses based on the TRIAS specificiation). It will be hard to then test not only the technical but also the business aspect of the data (does the data even make sense & what weird constellations can appear?).

Maybe testing can depend on a combination of mocked and actual TRIAS data. I just think that the unavailability of a TRIAS provider should not result in failing tests.