Add Vesuvio fit test for when Kfse is free parameter.

Refs #7492
Update Vesuvio system tests due to optimizer changes.

Refs #7492
Add Vesuvio Fitting test including a background.

Refs #7492
Fix silly copy-and-paste error in VesuvioTest reference file

Refs #7492
Relax tolerance on windows/mac for vesuvio tests.

The results are still acceptable they just differ slightly
(my guess is the GSL) from Linux where the reference file was created.
Refs #7492
Relax Mac tolerance. Refs #7492
Merge remote-tracking branch 'origin/feature/7492_background_in_compton_scattering'