When using the designer as a stand alone application and the renderer/preview in the
user application, the preview window would have to be closed and opened again every
time a change was made to the report.
This change adds an optional QFileSystemWatcher to monitor changes to the report file
and automatically refreshes the preview in the application when it is saved.
It may be turned on using the new parameter to ReportEngine::loadFromFile().
If the preview window is open in the application and the file name changes or the file is
removed, inform the user and close the preview window.
