The signal `void currentIndexChanged(const QString &text)` is obsolete in Qt6.
Instead, one should obtain the index and then use `QComboBox::itemText` to get
the text.

As recommended by
https://google.github.io/styleguide/cppguide.html#The__define_Guard

Correct .h file header comments: "Declares" -> "Defines". Also remove include comment "inheriting from". This resolves #1550.

finer sorting of include's (C before C++)

Made include guards uniform, using the command sc-intern/edit-scripts/update-include-guards.py Core Fit GUI/coregui GUI/crashhandler/

JobResultPresenter now recognizes JobItem valid for fitting and adds FitComparisonWidget to the list of available presentations.

New FitComparisonWidget (intended for real data/ simulated data comparison) is connected with JobResultsPresenter.