re 8313: SANS2D Reduction in GUI mode

This commit covers all the calls and settings used from SANS interface to
reduce data in Single mode and in Batch mode.
re 8313: SANS2D Reduction in GUI mode aux files

It is better to have the mask and the batch input as normal files. This
make life easier for future testers.
re 8313: rename test to follow name convention so far

new name: SANS2DReductionGUI.py
re #8313: Adjust systemtest SANS2DReductionGUI

Ticket #8245 organized the return methods to not return all the variants
for LOG and LIN.
re #8313: SANS2DReductionGUI code small organization
re #8313: SANS Reduction and adding runs

this systemtest provides coverage for adding runs using the add runs tab,
and also ensure that the resulting file can be reduced normally.
re #8313: SANS searching centre coverage

this systemtest ensure that the automatic searching centre algorithm works
for SANS2D data. It covers all the steps that is currently being used in
the UI.
Merge branch 'feature/8313_gui_reduction' into develop