Add event to notify the application that the shell application uses mouse.

lib/TerminalDisplay.cpp

@@ -2485,6 +2485,7 @@ void TerminalDisplay::setUsesMouse(bool on)
     if (_mouseMarks != on) {
         _mouseMarks = on;
         setCursor( _mouseMarks ? Qt::IBeamCursor : Qt::ArrowCursor );
+        emit usesMouseChanged();
     }
 }
 bool TerminalDisplay::usesMouse() const

lib/TerminalDisplay.h

@@ -596,6 +596,7 @@ signals:
     // QMLTermWidget
     void sessionChanged();
     void sizeChanged();
+    void usesMouseChanged();
 
 protected:
     virtual bool event( QEvent * );