Pycbc waveform generation

[wbenoit26]

This PR changes our waveform generation method from bilby to pycbc. Along the way, it also:

• Creates a new cosmology library to store whatever cosmological calculations we need. In particular, calculation of astrophysical volume now lives here, and there's now a DEFAULT_COSMOLOGY variable for standardization purposes.
• Updates rejection.py to generate waveforms using the from_parameter functionality
• Renames/rearranges some of the parameter ledger objects in a way that I think makes more sense. I tried to copy a bit from how pycbc organizes their ParameterLists
• Changes the theta_jn parameter distribution in priors.py to inclination to match what pycbc expects
• Changed phi_jl and phi_12 parameter distributions to be distributions over individual azimuthal angles of each object to allow for easier conversion to spin parameters that pycbc expects

To-do:

• [x] Test whether all of this works

Training and validation waveform generation ran, and testing waveforms are running now. The training run is here.

@EthanMarx there's still some work to be done on this, but I'd be interested in getting your feedback on the structure.

[EthanMarx]

This is awesome and long overdue. I'll take a look at the details in a bit, but it may make sense to just add the cosmology module to the utils library, especially since it's a single module with limited functionality currently. Will also keep our dependencies from getting too bloated. I'll leave it up to you though.

[wbenoit26]

I agree about the cosmology lib. I don't foresee us having many more functions that would fit in there. I'll move it into utils

[wbenoit26]

The testing finished up and the SV looks bad: https://ldas-jobs.ligo-wa.caltech.edu/~william.benoit/pycbc_waveform_sv.html. The training curves look good, and some quick checks of the testing waveforms look good, so I'm not sure what the issue is. I'll look into it some more.

[wbenoit26]

@EthanMarx I'm thinking that this PR might be a good place to start maintaining a dev branch

[wbenoit26]

@EthanMarx I'm going to open up a test PR so I can debug some of the container building issues that are happening here. I may also close this PR and create a new one that's a little more focused.

[EthanMarx]

Yeah - splitting this up into smaller PRs would be great. What's the core of the issue? Can you reproduce the container build failure locally?

[wbenoit26]

No, everything works locally, which is a challenge. Seems kind of sporadic, too - the data container build failed once out of nowhere on here. But yeah, I'll split this up.