Add classes to read in/out data from json data file (json format left to the user) instead of HistoXd

It is sometimes necessary to write results that are not histograms-friendly (fit results, statuses,...). After trying to patch the current HistoXd classes (adding number of entries per ABCStar chips and such while channels from all ABCStars are collected in single plots currently, making non-regular winnings,...) it became clear that having an output format/data representation that was not bound to be some HistoXd was the way to go. Here it is! JsonData provides a base class for this (does not do much...) while StarJsonData implements additional ancillary methods to e.g. sum up entries from all channels per chip or things like this. In addition to !432 (closed) of course one can then reload such objects to feed in analysis steps replacing or complementing data-taking results with external information.

@elebouli @VakhtangTsiskaridge(where are you ?)