Feed analysis steps using HistoFromDisk
- Implemented Histogrammer 'HistoFromDisk' and StdDummyTrigger/DataLoops to load histograms from disk in order to feed in analysis steps.
- Needed the possibility to pass json configuration to Histogrammer objects (done, could even be extended to all objects if need be).
- Corrected a few existing bugs in HistoXd classes' functions such as toJson()/fromFile().
Work done with @elebouli , initially from ITk Strips.