Creation of SANSWideAngleCorrection python api 2

re #6962
Update documentation SANSWideAngleCorrection

re #6962
Some improvements to SANSWideAngleCorrection

Progress reporting, and moving toward directives of python new api.

re #6962
Add unit test for SANSWideAngleCorrection

re #6962
Make the unit test independent of loading file data

it is required from the 'good practices' inside Mantid Team.

re #6962
Move documentation note to the usage section

The scientist suggested to put there. Now, that I'm aware of
WIKI_USAGE keyword, I decided to put inside the usage this note.

re #6962
Adjust the equations so to not break the qtassistant

re #6962
Remove the import SANSWideAngleCorrection from old python

re #6923
Merge remote-tracking branch 'origin/feature/6962_move_wide_angle_new_api'