Served the app icon from the icon theme in the new element wizard

The qet theme now lists Nuri's app icon PNGs under the name
qelectrotech, and the wizard loads its logo by that name instead of
the 256 px file path. The files stay in ico/breeze-icons/, where the
packaging scripts install them from.

Part of #1269.

sources/newelementwizard.cpp

@@ -25,6 +25,7 @@
 #include "qetmessagebox.h"
 #include "qfilenameedit.h"
 
+#include <QIcon>
 #include <QTreeView>
 #include <QVBoxLayout>
 #include <QLabel>
@@ -45,7 +46,7 @@ NewElementWizard::NewElementWizard(QWidget *parent, Qt::WindowFlags f) :
 	setWizardStyle(QWizard::MacStyle);
 #endif
 
-	setPixmap(LogoPixmap, QPixmap(":/ico/256x256/qelectrotech.png").scaled(64, 64, Qt::KeepAspectRatio, Qt::SmoothTransformation));
+	setPixmap(LogoPixmap, QIcon::fromTheme("qelectrotech").pixmap(64, 64));
 	setWindowTitle(tr("Créer un nouvel élément : Assistant", "window title"));
 	setButtonText(QWizard::NextButton, tr("&Suivant >"));
 	addPage(buildStep1());