Refs #8547. Methods to get run[s] label from ws and tests for them.
Refs #8547. Move sumWorkspaces to helper, fix it and add tests.

sumWorkspaces method was modifying the first workspace in the list
passed in, which caused problems.
Refs #8547. Make load() return the label.
Refs #8547. Use the returned label, create and store a group for it.

Instead of getting group name and retrieving it on every plot, we can
just store a pointer to the group.
Refs #8547. Remove unused functions.
Refs #8547. Different zero-padding width for ARGUS.
Refs #8547. Re-use logic of getLabel.
Refs #8547. Remove numerous Plus algorithm log messages.
Refs #8547. Better error-reporting.
Refs #8547. Check group membership by name, not pointer.

Otherwise we end up with multiple workspaces with the same name in the
group.
Refs #8547. Remove another unused function.
Refs #8547. Use the proper way to get zero padding for the instrument
Refs #8547. Merge 'origin/master' into 8547

Conflicts:
	Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/MuonAnalysis.h
	Code/Mantid/MantidQt/CustomInterfaces/src/MuonAnalysis.cpp
	Code/Mantid/MantidQt/CustomInterfaces/src/MuonAnalysisHelper.cpp
Merge branch 'feature/8547_muonanalysis_filenames' into develop