Use MWRunFiles in DGS Reduction GUI for the setting of the sample data file

[Russell Taylor]

Swap in the MWRunFiles widget (exposed to python in #7433) in place of the sample_label/edit/browse widgets in dgs_sample_setup.py.

This is a precursor to incorporating a live button into the MWRunFiles widget itself and using that here (see #5896).

[Russell Taylor]

Re #7442. Use MWRunFiles widget in DGS reduction GUI.

It has to be swapped in at runtime because: (a) pyuic doesn't know anything about MWRunFiles, & (b) there's a desire to have these GUIs runnable even from outside MantidPlot

Changeset: 3141cb0ae95305e0c104d6c732c807ae82efdb55

[Russell Taylor]

Re #7442. Add ability to set minimum width on the label.

Also expose this new method via python.

Changeset: 768ba6321c5d5d51c8ad6ed4eaacbefc817f4059

[Russell Taylor]

Re #7442. Apply minimum width to label in MWRunFiles widget.

This restores the alignment of the text edit boxes.

Changeset: 3ecbaf30ec0b816502b37a2a662020712c85bd37

[Russell Taylor]

Tester: Branch is feature/7442_mwrunfiles_in_dgs_reduction_gui

The top line of the first tab in the DGS Reduction GUI (created from the Interfaces menu item) is now the MWRunFiles widget if the GUI is run from within MantidPlot. This is the line labelled 'Sample Data'. The only observable differences should be the apparition of the validity asterisk with it's tooltip text and the hooking up of file validity to whether the QLineEdit's background is yellow or not (previously it only changed if the box was empty).

Check that file browsing, selection, typing all works correctly and that you can reduce a valid file successfully. Test the use of the 'Incident Energy Guess' lineedit as this shares some methods with the sample one.

[Andrei Savici]

Merge remote-tracking branch 'origin/feature/7442_mwrunfiles_in_dgs_reduction_gui'

[Stuart Campbell]

This ticket has been transferred to github issue ​8288