JetMonitoring allow EventHistoSpecs in SelectSpec
I have applied minimal changes to the JetMonitoringConfig in order to
- allow the definition of a SelectSpec with FillerTools = [ ..., EventHistoSpec(...), ...] which allows, for example, to monitor the number of jets for certain selections, and
- fix the duplicating of selection names in histogram names when loading 'external' SelectSpecs (i.e. outside of the current scope/config)