UI: Use signal when modifying groups settings

This commutes the vogleditor_settings class to a Q_OBJECT type and, following protocol, renames it to vogleditor_qsettings. The corresponding source files are subsequently renamed and the affected source files modified to use the new-named class.

The purpose of changing to vogleditor_settings to a Q_OBJECT is to allow its usage of Qt's signals and slots. It is now registered to get notified when a settings dialog object (vogleditor_QSettingsDialog class) changes and additionally emits a signal that is caught by VoglEditor to update its tree display.