Sngls results plotting

[GarethCabournDavies]

Some changes were required to allow search including single-detector events to have sensible results pages

These changes are compatible with #4050

• hdfinjfind: add if statements as the pivot/fixed ifo doesn't make sense without timeshifts
• foundmissed plots: add maximum SNRs and minimum distances to the coloring schemes, as these are decisive in searches which include single-detector triggers
• ifar_catalog: events now may have really low ifar, so using minimum ifar as a limit to the x-axis no longer makes sense
• page_foreground: changes are basically to remove the requirement to say coincs from the code
• page_ifar: change gets rid of the legacy files support
• page_snrifar: change fixes an issue where open-box values could be inferred from closed-box plot limits