Refs #8702. Clean-up tests: make checkProperty method private.
Refs #8839. Add tests for AutoGroup option.

Single period one is passing. Multi period one is not, which is the
problem in the current code (#8835).
Refs #8839. Remove old grouping code and clean-up a bit.
Refs #8839. Remove commented code from the tests.
Refs #8839. Refactor grouping loading method.

It now returns the grouping, so that we can use it outside the method.
Refs #8839. Make test more robust against exceptions and fix typo.
Refs #8839. Add grouping code
Refs #8839. Fix the multi-period grouping.

For some reason, previous implementation was returning grouped
workspaces as OutputWorkspaceN while still returning ungrouped
workspaces as OutputWorkspace. I don't really understand why we would
need OutputWorkpsaceN properties at all when we can just return a
group.
Refs #8839. Remove unused variable declarations.
Merge remote-tracking branch 'origin/feature/8839_loadmuonnexus_autogroup_using_muongroupdet'