Enhance stat vs FAR plots on the offline analysis summary page to include all event types and singles fit lines

[tdent]

At present the stat/FAR plots appear separately for each coinc or single event type, but that does not allow us to easily compare how the coinc backgrounds line up against each other, or against the singles fits / extrapolations. There is a nice multi-event-type FAR-stat plot in the methods paper https://arxiv.org/abs/2203.08545 which does so. Extend the SNRIFAR plot code to allow for this and make it part of the standard plotting workflow.

Specifically, this would allow us to diagnose possible cases where the FAR at high stat values might be dominated by singles fit extrapolation (which would hurt sensitivity at a given combined FAR for coincs) - or indeed unduly dominated by any event type.