exploration of a new monitoring facility

This MR introduces a Gaudi::Monitoring::Hub component for handling all sorts of monitoring. One can register monitoring Entitys to it (sources of monitoring), as well as Sinks (targets). All Entities are sent to all Sinks, but they have a type which allows Sinks to select the ones they want to handle. Sinks are then free to "log" in any format, e.g. to std::cout or to a json/xml/whatever file. In case of histograms, the Sink can save to Root file typically.

All details on the json format is in the comments of the Monitoring::Hub component here

The logging of existing counters have been moved to the new schema resulting is slight changes in the ref files, mainly a move of the counter logging within the output. The content of the counter lines has been left untouched for the moment. Later we may want to switch from text to structured out put, like json.