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.
Merge branch 'feature/8349_muon_plot_moving' into develop