Fit options for SANS Reduction transmission

this commit provides a more flexible way to deal with the fit for the
transmission for SANS reduction.

Now, you can set the option for the transmission and select a different fit
option for the can, or for the sample.

This commit does not change anything. It just rearranges things, to prepare
the path to the introduction of more fit options and to use different fit
options for each transmission.

re #7733
Extending fit/trans to allow selector sample|can

Process user file to allow defining fit/trans/can or fit/trans/sample
providing different fit settings for can or sample.

It provides query methods to define fitMethod, lambdaMin and lambdaMax,
that will be used by the GUI.

re #7733
Extend SANS UI to allow providing different fitting settings

Now, you can provide different options for CAN or SAMPLE when

fitting transmissions.

re #7733
remove CALC_TRANS_FIT_PARAMS attribute

re #7733
Introduce support for Polynomial fit for calculate transmission

re #7733
Adjust isis_reduction_steps to support polynomial for trans

re #7733
Extend SANS GUI to support Polynomial

re #7733
Adjust SANS interface to read settings for can and sample

re #7733
Correct the label of SANS INTERFACE

Change CAN to Can, to avoid confusion of thinking of acronym CAN.

re #7733
Merge remote-tracking branch 'origin/feature/7733_sans_fit_trans'