LatencyScan publishing histograms via DQM

Edits to LatencyScan to be able to run in dual process mode and publish histograms via DQM. Note that I have left two major functions (ScanLatency and ScanStubLatency) which are used only by MPALatency.cc and rely on the histograms directly outputted from the functions. I put these at the bottom of the file, wrapped in an if USE_ROOT. I think that ideally these should be removed eventually to avoid duplication since they are otherwise doing the same thing.