[TD]Centralize preference getters

src/Mod/TechDraw/Gui/QGICenterLine.cpp

@@ -33,6 +33,7 @@
 #include <Base/Console.h>
 #include <Base/Parameter.h>
 
+#include "PreferencesGui.h"
 #include "QGICenterLine.h"
 
 using namespace TechDrawGui;
@@ -71,10 +72,7 @@ void QGICenterLine::setBounds(double x1,double y1,double x2,double y2)
 
 QColor QGICenterLine::getCenterColor()
 {
-    Base::Reference<ParameterGrp> hGrp = App::GetApplication().GetUserParameter()
-        .GetGroup("BaseApp")->GetGroup("Preferences")->GetGroup("Mod/TechDraw/Decorations");
-    App::Color fcColor = App::Color((uint32_t) hGrp->GetUnsigned("CenterColor", 0x00000000));
-    return fcColor.asValue<QColor>();
+    return PreferencesGui::centerQColor();
 }
 
 Qt::PenStyle QGICenterLine::getCenterStyle()