QmlProject: Search for qmlviewer in configured Qt versions (if not found in $PATH)

If no 'qmlviewer' executable is found in the PATH, iterate through the
list of configured Qt versions and try to find a qmlviewer there. This
should help users configuring creator such to play with Qml.

Right now the first qmlviewer found in a Qt version is selected. A UI
to let the user select one explicitly was not possible any more (string
freeze).

This requires a dependency from QmlProjectManager to
Qt4ProjectManager.

Reviewed-by: dt

src/plugins/qmlprojectmanager/qmlprojectrunconfiguration.h

@@ -88,18 +88,19 @@ public slots:
     void changeCurrentFile(Core::IEditor*);
 
 private slots:
-
     QString mainScript() const;
     void setMainScript(const QString &scriptFile);
     void updateFileComboBox();
 
+    void updateEnabled();
+
     void onViewerChanged();
     void onViewerArgsChanged();
     void onDebugServerAddressChanged();
     void onDebugServerPortChanged();
 
-
 protected:
+    QString viewerDefaultPath() const;
     QmlProjectRunConfiguration(Internal::QmlProjectTarget *parent, QmlProjectRunConfiguration *source);
     virtual bool fromMap(const QVariantMap &map);
     void setEnabled(bool value);
@@ -114,7 +115,6 @@ private:
 
     QString m_scriptFile;
     QString m_qmlViewerCustomPath;
-    QString m_qmlViewerDefaultPath;
     QString m_qmlViewerArgs;
     QmlProjectRunConfigurationDebugData m_debugData;