Documentation BEC Widgets

The documentation of Slot/SafeSlot in https://bec.readthedocs.io/projects/bec-widgets/en/latest/developer/widget_development/bec_dispatcher.html should be improved. It should explain the difference between Slot and SafeSlot, when to use which and the documentation for how to create a callback function is potentially missleading. If SafeSlot is used, the try/except (https://gitlab.psi.ch/bec/bec_widgets/-/blob/main/bec_widgets/qt_utils/error_popups.py?ref_type=heads#L23) can lead to a silent failure if the the wrong arguments are specified. So the documentation should be "This function must accept two parameters: msg_content...` instead of should usually...