re #8245: sans trans fit option

Correct the isis_reduction_steps to process properly the FIT trans option.
Bugs found:

1 - Setting an option for 'both' (can and sample) did not override previous
settings for them alone.
2 - Returning from fitMethod return many variants (LIN, LINEAR, ...). It
is better to return just one variant of the same method (LINEAR, LOGARITHMIC, and PolynomialX)
3 - Add a method to check if the trans was set using the specific selectors (sample and can).
re #8245: sans trans fit option SANSRunWindow

Correct the SANSRunWindow to process properly the FIT trans option.

1 - Separate the loading Trans settings and the selector changing option.
2 - Correct the option to identify fit on/off
3 - Correct the parser of the fitMethod for CAN
Merge remote-tracking branch 'origin/master' into bugfix/8245_sans_trans_option
Merge remote-tracking branch 'origin/bugfix/8245_sans_trans_option'