Enable reweighting of kinematics term by cosmology

[jiwoncpark]

Probe response of D_s/D_{ds} = \sigma_V^2 / J(\xi_lens, \xi_light, r_ani) to number of points in \xi_lens, \xi_light, r_ani space. Then compute posterior by weighting \sigma_V^2 ~ N(measured_\sigma_V^2, measured_\sigma_V^2_err^2) by J. See Eq. 9 of https://arxiv.org/pdf/1809.01274.pdf for details.