Destroy the MainWindow only on a clean exit
- works around a problem with std::exit(0)
- removed HAVE_RUN_MENU compiler flag
- corrected a comment
Added console output to windows
- in the win32 tray-monitor.pro file: added CONFIG += console
  this will lead to a regular console output when the monitor is run in
  the console but a fast flashing up console when run from the explorer
  by double-click
- output via std::fprintf instead of qDebug() since this did not have
  an effort
Provide a replacement for the std::exit() handler as workaround
- This is probably the saftest way to delete the Qt objects in
  the qt-tray-monitor. There is now a replacement of the void exit(int)
  that gets linked instead of the one in the C-library. This "overloaded"
  function is deleting the qt objects first and then calling _exit(int)
  to return to the kernel. This avoids a segmentation fault when the
  QCoreApplication wants to cleanup its children.
- Attention: Any cleanup handler registered with atexit() will not be called
  (fortunately there is currently no one registered)
Added SIGINT signal handler to handle ctrl+c
Added MessageBox to display help options under Windows
- removed CONFIG += console for Windows project file
- QApplication created on the head