Tests for build_and_store_phase_stats

[ArneTR]

The new functionality for the compare feature stores values in the phase_stats table.

Please prepare a scaffold for this test and then let's agree on a defined set of "expected results" to get a stable test.

As a starter use the demo data currently provided in the data folder, clear the phase_stats and try to get the same results by recalculating.

benefit of that would be that we directly test if our demo data is still current.