QT Viewer main structure.

CMake: added an entry at main CMake script that makes QTViewer an optional build.
QT Viewer main structure only, libQGLViewer or any 3D functionality can be added to mainWindow as a widget later on.

src/qtviewer/main.cpp

@@ -0,0 +1,25 @@
+
+#include <QApplication>
+#include <QString>
+#ifndef QT_NO_OPENGL
+#include <QGLFormat>
+#endif
+
+#include "mainwindow.h"
+
+int main(int argc, char **argv)
+{
+    QApplication app(argc, argv);
+
+	//QGLViewer viewer;
+
+   // Restore the previous viewer state.
+   //viewer.restoreStateFromFile();
+
+    MainWindow window;
+    //window.openFile("	");
+
+  window.show();
+
+  return app.exec();
+}