This reverts commit 5a21cabd.

gstlal_inspiral_marginalize_likelihoods_online: don't accumulate background samples since they are already drawn from a cumulative distribution

- not just LR factor

- function barfed if tlo and/or thi is a non-float value.
- refs #2505

- latex barfed on "D_H" in y axis label
- tweak title while at it.
- refs #2505

- all places where this plotting function is used need to invoke snr_joint_pdf_keyfunc() to pre-process the parameters, move that into this function so that the plot title reflects the actual measured horizon distances.

- list the dependencies in alphabetical order