Add histogram sink to Escher for new TrackMonitor format

Recent changes to TrackMonitor mean that these monitoring plots are no longer output to the histograms.root output file, and instead require a separate histogram sink to operate. This update adds the sink.

Sink needed for: TrackMonitor, TrackVertexMonitor, UTTrackMonitor; ( Rec!2565 (merged) ) FTTrackMonitor ( Rec!2608 (merged) )