QmlProject: Add mainFile property

The mainFile property of QmlProject is the default file to run. People
have still the opportunity to override this in their run settings,
though.

The wizard generated code was updated accordingly. Note that this makes
projects generated by the wizard incompatible with QtCreator 2.1!

Task-number: QTCREATORBUG-3249

src/plugins/qmlprojectmanager/fileformat/qmlprojectitem.h

@@ -25,6 +25,7 @@ class QmlProjectItem : public QObject {
     Q_PROPERTY(QDeclarativeListProperty<QmlProjectManager::QmlProjectContentItem> content READ content DESIGNABLE false)
     Q_PROPERTY(QString sourceDirectory READ sourceDirectory NOTIFY sourceDirectoryChanged)
     Q_PROPERTY(QStringList importPaths READ importPaths WRITE setImportPaths NOTIFY importPathsChanged)
+    Q_PROPERTY(QString mainFile READ mainFile WRITE setMainFile NOTIFY mainFileChanged)
 
     Q_CLASSINFO("DefaultProperty", "content");
 
@@ -43,10 +44,15 @@ public:
     QStringList files() const;
     bool matchesFile(const QString &filePath) const;
 
+    QString mainFile() const;
+    void setMainFile(const QString &mainFilePath);
+
+
 signals:
     void qmlFilesChanged(const QSet<QString> &, const QSet<QString> &);
     void sourceDirectoryChanged();
     void importPathsChanged();
+    void mainFileChanged();
 
 protected:
     QmlProjectItemPrivate *d_ptr;