Remove the inheritance from TrackPerson in favor of composition, this allows a better handling of interactions with the TrackPerson as changes now go through defined interfaces.

Main changes:

TrackPerson no longer is a QList<TrackPoints>
TrackPerson now has a QList<TrackPoints
new function deleteFrameRange which will delete a range of frames, but leaving no gaps in the middle
lastFrame is now compute and not stored, hence no need to update it
firstFrame is set when creating a TrackPerson and will be updated when needed automatically

Reviewer Checklist

Formatting

the pre-build checks succeed

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()