Remove usage of deprecated types of Qwt

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Closes #215 (closed), #207 (closed)

Reviewer Checklist

General code quality

• naming conventions are met (see .clang-tidy for detailed information)
• no static analyzer warnings in new code parts (e.g., use clang-tidy for checking)

General usability

• old versions of pet-files are still loadable

Only if changes in UI

• new elements are also saved and loaded from pet-file
• check if tab order is still correct
• all new SpinBoxes are promoted
• new keybindings added to Petrack::keyBindings()

added documentation tooling labels

changed the description

marked the checklist item new elements are also saved and loaded from pet-file as completed

marked the checklist item all new SpinBoxes are promoted as completed

marked the checklist item new keybindings added to Petrack::keyBindings() as completed

marked the checklist item check if tab order is still correct as completed

marked the checklist item old versions of pet-files are still loadable as completed

marked the checklist item naming conventions are met (see .clang-tidy for detailed information) as completed

marked the checklist item no static analyzer warnings in new code parts (e.g., use clang-tidy for checking) as completed

approved this merge request

merged

mentioned in commit de448412