added lensed_binary_neutron_star and renamed lensed_bbh to lensed_binary_black_hole

In order to include binary neutron star analyses and work with waveform-approximant = IMRPhenomPv2_NRTidalv2, I included a lensed_binary_neutron_star_model in golum/golum/golum/tools/waveformmodels.py. I also renamed lensed_bbh_model to lensed_binary_black_hole_model for consistency (the complete name needs to be in the definition for it to be parsed correctly by bilby)