Read multiple injection files and different parameterizations

This is a pretty big omnibus change that adds a bunch of functionality.

• Multiple injection files can be passed and they will be combined based on the stored total_generated/sampling_time` to make sure each file is equally weighted. This is done in the collection stage and a downsampled file is saved locally as is done for the posterior samples.
• Additional parameterizations are supported. For masses these include flat-detector (previous, m1-q), chirp-mass (mc-q), primary-secondary (m1-m2) and spins component (a1, costilt1, ...), aligned (chi_1, chi_2, aka spin1z, spin2z)

@jacob.golomb @shanika.galaudage @amanda.farah this probably pretty badly clobbers changes you've been working on, apologies that I didn't open this earlier.