[ESSDIFFRACTION, BEER] Add correction to loaded McStas NeXus files

[celinedurniak]

• Modify loader of simulated BEER data (NeXus file from McStas) for the pulse shaping modes of operation of the choppers (modes 4-6 in Mcstas convention). See the enclosed notebook for an example of implementation
• Add L2 (sample - detector distance for each pixel in the loaded data array)
• Add option to load all the detector banks at once

pr_beer_loader_sciline.ipynb

Input files to run the notebook: duplex sample and Vanadium NeXus files from McStas simulations (mode 4 for the choppers, 500x500 resolution for each of the detector panels) stored on NextCloud: https://project.esss.dk/nextcloud/index.php/f/21246100