FitSettingsDialog class should support several FitContainer instances

[Neverhorst]

What is affected by this bug?

FitSettingsDialog can only control/configure a single FitContainer instance.

When does this occur?

When trying to use multiple FitContainer instances in a measurement logic you only want a single FitSettingsDialog to configure them all simultaneously.

Where on the platform does it happen?

FitSettingsDialog.__init__ only takes a single FitContainer

Expected behavior (i.e. solution)

FitSettingsDialog.__init__ could optionally take an iterable containing FitContainer instances. Most instance methods would need to be adjusted to this change.