Resolve "Ease usage of c3d visualization for time synchronization"

This MR adds a new dialog to edit the time offset (and in future position and rotation) of motion capturing data.

The dialog is accessible over File > Edit MoCap Settings

(the Time is there for distinguishement to the future Position and Rotation)

As requested in the issue, the dialog is usable alongside the main window and changes are immeadiately shown.

Also, the option to select mocap persons to show was added (the show checkbox). This option is saved in the pet file.

The time offset part of the mocap file dialog was removed since the functionality is now available through the new dialog.

Closes #391 (closed)

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()