Fix non portable names in the package

Output from package check:

Found the following files with non-portable file names:
  R/1-Chargement_data - RADIS CAWET_sanstextures.R
  R/2-Simulations - SIMCAWET_sanstextures.R
These are not fully portable file names.
See section ‘Package structure’ in the ‘Writing R Extensions’ manual.

Spaces are not recommanded in file names for portability on different OSs.