Feature to indicate whether there are any 'outlier' sites

[shaziaruybal]

Feedback from the DRpower/pfhrp2/3 planner workshop was that it would be nice if we could output an indication of 'outlier sites' - eg if certain sites have high prevalence but overall province-level prevalence is low and/or below threshold. This could serve as a warning flag for sites that should be monitored or followed up.