The test aggregation plugin's dependencies are outdated

It is outdated, because:

• cif.cifm2crl2 no longer has tests.
• cif.datasynth, cif.multilevel, cif.plcgen, common.app.framework and common.emf now also have tests.

I think we should:

• Make sure all test projects, and only test projects, are dependencies.
• Have an automatic check, so that we get notified if it goes out of sync again. Probably a unit test in the test aggregation project will work.

I found this issue while working on !1121 (merged). By sheer luck it didn't break the build order there, so I'll solve it here in a separate issue. That merge request was large/complex enough already.