Freeze theory no longer works

[rozyczko]

1. create a theory
2. try to freeze it
3. TypeError: can't pickle QLineEdit objects

This comes from the recent addition of plot sliders. Each data/theory item contains now a QLineEdit object, which is not copyable.
copy.deepcopy in cloneTheory() will have to be replaced with a more complex method, allowing for copying of QObject derived types.

[rozyczko]

Alternatively, can we simplify the slider storage so it just keeps its max/min numerical values in the model item rather than the whole line edit object?

[rozyczko]

Cloning a QObject is not really feasible https://stackoverflow.com/questions/2855495/qobject-cloning

This means we can either do it manually, copying fields one by one or, again, refrain from keeping a QObject inside Data1D/Data2D structures.

[butlerpd]

Is this the same issue as #1418? I note that @ajj says he had to revert to 4.x for his demo because he needed the freeze theory and it was not working for him. We should probably #1418 if this supersedes?

[rozyczko]

Nope. This is a new issue, recently fixed in PR #1891

[butlerpd]

Thanks @rozyczko - This was not linked to the PR which was closed today so I am closing this ticket.