Restructure tests

.coveragerc

.gitlab-ci.yml

setup.cfg

test/context.py

test/core/__init__.py

test/core/example_test.py

test/core/grid_test.py

test/core/likelihood_test.py

test/core/prior/__init__.py

test/core/prior/analytical_test.py

test/core/prior/base_test.py

test/core/prior/conditional_test.py

test/core/prior/dict_test.py

test/core/prior/interpolated_test.py

test/core/prior/joint_test.py

test/core/prior/prior_files/GW150914_testing_skymap.fits

test/core/prior/prior_files/aligned_spins_bbh.prior

test/core/prior/prior_files/aligned_spins_bbh_tides_on.prior

test/core/prior/prior_files/aligned_spins_bns.prior

test/core/prior/prior_files/aligned_spins_bns_tides_on.prior