clean-up, add unit tests for psd + kernels modules

gstlal-burst/bin/gstlal_cs_triggergen

gstlal-burst/python/snax/pipeparts.py

gstlal-inspiral/python/cbc_template_fir.py

gstlal-inspiral/python/svd_bank.py

gstlal-ugly/bin/gstlal_ninja_median_of_psds

gstlal-ugly/bin/gstlal_ninja_smooth_reference_psd

gstlal-ugly/python/metric.py

gstlal/bin/gstlal_asd_txt_from_psd_xml

gstlal/python/kernels.py

gstlal/python/plots/psd.py

gstlal/python/psd.py

gstlal/tests/tests_pytest/conftest.py

gstlal/tests/tests_pytest/test_kernels.py

gstlal/tests/tests_pytest/test_psd.py