QueryDTO.Value being classed as "any" meant DateAttempts would be
unmarshaled as map[string]any, so a custom UnmarshalJSON checks the data
type and unmarshals into a DateAttempt if needed. mentionedUers,
referrer and time matching implemented for activity search. Also, fixed
multi-class queries (e.g. date -and- bool for last-active).
only supports queries of fields actually in Activity. The web UI only
directly queries two of these, ID and Time (mistakenly referneced as date in
the web ui previously). Later commits will come up with creative ways of
dealing with all the other query types.
Harvey Tindall