hide the mainwindow when start minimized has been checked

This should have been done in the first place. This is the
convention on Windows when we start an application minimized
it should not be displayed on taskbar but only as an icon in
the notification area.

Change-Id: If867e70bfa48be0db3ce6f55ca63b9a9f91bc401
Tuleap: #760

main.cpp

@@ -143,8 +143,10 @@ main(int argc, char *argv[])
 
     if (not startMinimized)
         MainWindow::instance().show();
-    else
+    else {
         MainWindow::instance().showMinimized();
+        MainWindow::instance().hide();
+    }
 
     MainWindow::instance().createThumbBar();