New File Dialog: Choose right default project for adding

So far we used a heuristic that prefers .pro files in the same directory
as the new files. That fails if there are multiple .pro files in the
same directory. So instead introduce a mechanism to pass extra data
through the wizard.

Task-number: QTCREATORBUG-7157
Change-Id: I615f7292e16a0a6cb1e84f090016879f1038409f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

src/plugins/coreplugin/mainwindow.h

@@ -137,7 +137,8 @@ public slots:
 
     void showNewItemDialog(const QString &title,
                            const QList<IWizard *> &wizards,
-                           const QString &defaultLocation = QString());
+                           const QString &defaultLocation = QString(),
+                           const QVariantMap &extraVariables = QVariantMap());
 
     bool showOptionsDialog(const QString &category = QString(),
                            const QString &page = QString(),