Reorder tests for categorization, add block comments.
Reorder tests for categorization, add block comments.

- Tests are reordered according to category:
    - Important tests.
    - Not yet relevant tests.

- Block comments have been added, which desribe these tests.

- @pytest.mark.skipif added to 'Not yet relevant' category tests.

orbitfold/tardis,Tobychev/tardis,Tobychev/tardis,orbitfold/tardis,kaushik94/tardis,kaushik94/tardis,orbitfold/tardis,kaushik94/tardis,orbitfold/tardis,kaushik94/tardis,Tobychev/tardis