Multiple data files

[creuzige]

Add the ability to analyze several data files with the same instrument parameter and cif files.

Some brainstorming around this:

• Probably a pretty heavy revision, so it might be good to move this to a separate branch when testing, so as to not break other things.
• Not sure what the resulting analysis plots and table should look like. Some ideas: extra lines on a single plots? N extra plots? Option to select/scroll through a set of N plots?
• Add uncertainty measures based on repeated measurement. From our conversation on 18 May 2022, maybe this is built as another layer above the phase fraction uncertainty?
• Some type of plot/report roll up comparing the different measurements.

I think it's fair to tell users that changing the instrument parameter and/or cif files means a separate analysis.

[maxgarman]

Have option to show all datasets for both Intensity plots, as well as normalized intensity variation plot.