- prepare-all-data indexes data first by experiment, then by operators, using dictionaries
(instead of arrays)
- all the plots use getCurve( alldata, expseries, operator ) to retrive the correct curve
(instead of numerical index)
- added plot_several_curves and plot_several_measures

- suppressed the '        dict(selector="th:last-of-type", props=barright)' which just added a line at the end of the headers...
- added a parameter start, allowing to start counting the groups after a number of lines
- added an initial bar for this number of lines