xmm extension

new variable in utils.py functions: instrument = ‘xmm’ or ‘nustar’ in: → read_one_matrix → make_tphase → make_enphase → elaborate_pulsed_fraction (just for the energy range: [0.5,10] maybe put as max 12)

new functions in utils.py: → GTI filtering for xmm, in make matrix functions: create_initiate_sas(..): creates the sas_init.sh for the sas environment filter_evt_evselect(..): executes sas_init.sh and ev_select → backscale correction used in make matrix functions: backscale_correction: User gives path to spectra to retriever BACKSCAL. If not given, it tries anyway find_file(..): finds a file. Used in backscale_correction. Maybe should be moved to process