Simplify string constants

GUI/Models/ResolutionFunctionItems.cpp

@@ -34,8 +34,8 @@ ResolutionFunctionNoneItem::createResolutionFunction(double) const
 
 /* --------------------------------------------------------------------------------------------- */
 
-const QString ResolutionFunction2DGaussianItem::P_SIGMA_X = QString::fromStdString("SigmaX");
-const QString ResolutionFunction2DGaussianItem::P_SIGMA_Y = QString::fromStdString("SigmaY");
+const QString ResolutionFunction2DGaussianItem::P_SIGMA_X = "SigmaX";
+const QString ResolutionFunction2DGaussianItem::P_SIGMA_Y = "SigmaY";
 
 const QString ResolutionFunction2DGaussianItem::M_TYPE = "ResolutionFunction2DGaussian";