Refs #8349. Made floating window placement a bit smarter.

We are still cascading, but is previous place is free - we use it again.
Refs #8249. Don't delete existing workspace and close it's plot.

The workspace will get overwritten and it will cause existing plot to be
updated automatically.

Plus refactored a function, as with mentioned functionality removed it
looked too big for what it was doing.
Refs #8349. Don't plot ws again if plot already exists.

Just make sure the plot is visible in that case. It should've been updated
automatically.
Refs #8349. Use plotSpectrum for setting plot style.

As we can now plot to the same window, no need to set style parameters
manually.
Refs #8349. Removed big function which wasn't actually needed.
Refs #8349. Use plotSpectrum instead of checking/plotting manually.
Refs #8349. Made plotSpectrum get plot style params itself.
Refs #8349. Removed unused closePlotWindow.
Refs #8349. Quick fix for the problem I've found.

Don't show fitting results in the workspace selector on DA tab. When
fitting is done, they do get deleted before creating a new ones. Property
browser is subscribed to deletion events but not to addition events, which
causes problems in that case.
Refs #8349. Don't show all graphs when uncheking "Hide prev. graphs"

As now they all share the same place, when all shown they are hidden behind
a single graph.

That's a simple solution, need to discuss whether scientists want something
different to happen.
Refs #8349. Merge remote-tracking branch 'origin/master' into 8349

Conflicts:
	Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/MuonAnalysis.h
	Code/Mantid/MantidQt/CustomInterfaces/src/MuonAnalysis.cpp
Refs #8349. Fixed Qt warnings.
Refs #8349. Got rid of all the wsIndex uses.

It was needed because for some reason previously workspaces with group
held the data of all the groups, not just for the one. In one of the
tickets I've fixed it so now we should always have one wsIndex only.
Refs #8349. Removed function accidentally left after merge.
Refs #* (no branch, rebasing master). Refs #* master. Merge remote-tracking branch 'origin/feature/8349_muon_plot_moving'