[NbtkGtkExpander] fix spacing and positioning issues
[NbtkGtkExpander] fix spacing and positioning issues

jonnylamb/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,pwithnall/mx,clutter-project/mx,jonnylamb/mx,clutter-project/mx,pwithnall/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx