Support existing Qml project for "standalone" Qml apps

Now, the user can select an existing qml application that can
be turned into a standalone Qml app. The qml source files will not
be copied around but rather stay in their original location. The
new .pro file that gets generated by this wizard will reference
the qml source files via relative path and deploy them from there.

Task-number: QTCREATORBUG-1814

src/plugins/qmlprojectmanager/wizards/templates/cpp/main.cpp

@@ -5,7 +5,7 @@ int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
 
-    QmlApplicationView qmlApp(QLatin1String("app.qml")); // MAINQML
+    QmlApplicationView qmlApp(QLatin1String("qml/app/app.qml")); // MAINQML
     QStringList importPaths; // IMPORTPATHSLIST
     qmlApp.setImportPathList(importPaths); // SETIMPORTPATHLIST
     qmlApp.setOrientation(QmlApplicationView::Auto); // ORIENTATION