Vertex compare modifications for PV resolution monitor

A data PV resolution monitor was added to RecoMon for two sets of PVs reconstructed from 2 random subsets of HLT1 and HLT2 Velo tracks.

Some changes are needed in the VertexCompare.cpp for the monitor to work:

• All histograms are changed to Gaudi::Accumulator::Histograms
• m_monitoring gaudi property is added for the monitoring histograms: pulls and arrays of Gaudi histograms for the differences in matched PV positions: dx, dy, dz for each bin on nTracks. Later these histograms will be processed in AutomaticAnalysis to obtain PV resolution in each dimension and show it in the Monet
• m_requireSingle is added, to make offline plots based on the events with one PV
• Two new algorithms to split HLT2 tracks randomly into two subsets are added

Needed for MooreOnline!406 (merged), Moore!3312 (merged)

Goes with Allen!1563 (merged), Moore!3542 (merged)