gstlal-inspiral: include SNR joint PDFs in ranks, new FAP and FAR machinery

this patch folds the joint SNR PDFs into the ranking statistic.  in doing
so, it breaks the current technique for building the ranking statistic
histograms and therefore also introduces a new technique for constructing
those histograms based on stochastic sampling.

this patch also fully reworks the FAP and FAR machinery.  it introduces new
on-disk file formats, combines all instrument categories into a single
experiment with a single FAP, redesigns the FAR normalization around a
single total event count (removing the trials table machinery, using the
coinc parameter histogram data instead).

some steps in the pipeline become more costly.
gstlal_inspiral_calc_likelihoods now requires several CPU cores to run the
stochastic sampling in the background while assigning likelihood ratios in
the main thread.  other steps become less costly.
gstlal_inspiral_marginalize_likelihood is reduced to little more than file
I/O.