Mass dependent spin magnitude
This patch adds mass-dependent spin magnitude distributions in order to support mmax-model-selection work. Specifically, it adds
BetaSpin1MagnitudeGivenMass1BetaSpin2MagnitudeGivenMass2
which rely on BetaSpin*Magnitude but condition on mass1_source and mass2_source, respectively.
Separate parameters for each Beta distribution are supported.
Edited by Reed Essick