Define WSJT-X manual URL in a single place.

Since the manual URL is used in both the installer and the WSJT-X code
the definition of  the URL (CMake variable  PROJECT_MANUAL) is defined
in  the  CMakeList.txt file  and  propagated  to  the source  via  the
wsjtx_config.h header.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@4252 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

mainwindow.cpp

@@ -994,9 +994,7 @@ void MainWindow::msgBox(QString t)                             //msgBox
 
 void MainWindow::on_actionOnline_Users_Guide_triggered()      //Display manual
 {
-  QDesktopServices::openUrl(QUrl(
-                                 "http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main.html",
-                                 QUrl::TolerantMode));
+  QDesktopServices::openUrl (QUrl (PROJECT_MANUAL, QUrl::TolerantMode));
 }
 
 void MainWindow::on_actionWide_Waterfall_triggered()      //Display Waterfalls