[JUNGFRAU] Fixing JFstrixel LUT mask import error
Description
@pfaeffle encountered an import error of strixel LUT mask, which were not included in standard installation as they were missing in setup.py file. We also suggest to change the method how the LUT mask is imported in jfstrixel.py According to this: https://dev.to/bowmanjd/easily-load-non-python-data-files-from-a-python-package-2e8g using importlib.resources is more reliable and robust solution comparing to file method.