EQSANS UI fixes

[Mathieu Doucet]

• Check that all the data files can be found before starting the reduction.
  
• Only keep the dark current on the first tab, and use that value everywhere else.
  
• Get rid of the "number of sub-pix" for I(Q) output.
  
• Change Log check box to radio buttons, and spell out "Linear Q binning" and "Log Q binning"

[Mathieu Doucet]

Also: combine sample and background tabs

[Mathieu Doucet]

In [13209]:

Remove n_sub_pix option. Add lin/log radio. Re #3371

[Mathieu Doucet]

In [13226]:

Tie sensitivity dark current to sample dark current. Re #3371

[Mathieu Doucet]

In [13233]:

Tie transmission dark current to sample dark current. Re #3371

[Mathieu Doucet]

In [13246]:

Tie bck transmission dark current to sample dark current. Re #3371

[Mathieu Doucet]

In [13271]:

Check that files exist when the reduction is set up rather than at exec time. Re #3371

[Mathieu Doucet]

Everything has been done except combining the sample and bck tabs. This will be dealt with in ticket #3384

[Michael Reuter]

I have looked over the UI and changelogs and it looks like all the requested work has been done.

[Stuart Campbell]

This ticket has been transferred to github issue ​4218