Helical: add a dedicated widget for `nabu-helical-prepare-weights-double`

...dgets/reconstruction/NabuHelicalPrepareWeightsDoubleOW.py

...gets/reconstruction/icons/nabu_prepare_weights_double.png

...gets/reconstruction/icons/nabu_prepare_weights_double.svg

...truction/test/test_nabu_helical_prepare_weights_double.py

tomwer/core/process/reconstruction/nabu/helical.py

tomwer/core/process/reconstruction/nabu/utils.py

tomwer/core/scan/hdf5scan.py

tomwer/core/scan/helicalmetadata.py

tomwer/gui/qlefilesystem.py

tomwer/gui/reconstruction/nabu/helical.py

tomwer/gui/reconstruction/nabu/nabuconfig/preprocessing.py

tomwer/gui/reconstruction/nabu/test/test_helical.py