Expose advanced features of LoadSQW through PV Plugins

[Owen Arnold]

LoadSQW can use a disk-based back-end now #3586. This doubles, up as a MD nexus file made on the fly, which may be useful post-visualisation. We should expose these options via the PV SQW reader because it uses this algorithm under the hood.

[Owen Arnold]

In [14957]:

Exposed using exising "Load In Memory" option on PV filter. refs #3840. Have modified unit tests, but have purposefully not included a test which makes a file back-end as this would create the file in the versioned autotest directory and cause problems down the line.

[Owen Arnold]

In [14958]:

Fix GCC tests refs #3840.

[Owen Arnold]

In [14959]:

Fix GCC tests refs #3840.

[Owen Arnold]

In [14960]:

Fix GCC issue with tests refs #3840.

[Owen Arnold]

For testing purposes. Load an SQW file in ...\Test\Vates into paraview.

• Leaving 'Load In Memory' Unchecked will result in a nxs file with the same name going into the same directory as was loaded from.
• Checking 'Load In Memory' will NOT result in a nxs file being created in the AutoTestData directory

The loaded result should look the same and be used the same via either route. Also the generated nxs file should be tested to ensure it can be loaded into Mantid using LoadMD.

[Michael Reuter]

All of the requested checks work as expected.

[Stuart Campbell]

This ticket has been transferred to github issue ​4687