Make Labels keyboard shorcuts configurable by end user into KDE config panel...

Make Labels keyboard shorcuts configurable by end user into KDE config panel of each root digiKam window.
This include Rating, Color, and Pick Labels.
Unlike tag action shortcuts which are stored in digiKam DB, Labels action shortcuts are stored in each
XML GUI config file of each root digiKam window.
Because each root window manage shortcut individually for relevant GUI, you need to apply a keyboard shortcut
change in each root window setup, to be homogenous everywhere.
BUGS: 313856
FIXED-IN: 4.0.0