Qt5: don't use native color dialog

src/Gui/Widgets.cpp

@@ -748,6 +748,9 @@ void ColorButton::onChooseColor()
 #endif
         QColor currentColor = d->col;
         QColorDialog cd(d->col, this);
+#if QT_VERSION >= 0x050000
+        cd.setOptions(QColorDialog::DontUseNativeDialog);
+#endif
 
         if (d->autoChange) {
             connect(&cd, SIGNAL(currentColorChanged(const QColor &)),
@@ -771,6 +774,9 @@ void ColorButton::onChooseColor()
         if (d->cd.isNull()) {
             d->old = d->col;
             d->cd = new QColorDialog(d->col, this);
+#if QT_VERSION >= 0x050000
+            d->cd->setOptions(QColorDialog::DontUseNativeDialog);
+#endif
             d->cd->setAttribute(Qt::WA_DeleteOnClose);
             connect(d->cd, SIGNAL(rejected()),
                     this, SLOT(onRejected()));