fix typo slice_indexes vs slice_index. slice index was never loaded so middle slice was always reconstructed

# Conflicts:
#	tomwer/core/process/reconstruction/axis/axis.py

start adding intensity normalization

See merge request tomotools/tomwer!335

gui: improve reconstruction parameters: add tooltip of the url on the reconstruction parameters overview

* remove calculation area (volume for now)
* remove calculation method (one value per frame...)

# Conflicts:
#	tomwer/core/scan/scanbase.py