MAINT: Separate adding SNRs per IFO to a sample into a new function
requested to merge rhiannon.udall/bilby:feature/compute-ifo-snrs-for-conversion-in-likelihood into master
Moves code snippet which adds IFO snrs to a sample into a separate function within the Likelihood. Thus different likelihoods may define this differently if they have different SNRs which must be computed.