Comment 3 for bug 1393199

Have to do some more testing, but I believe it's due to when the ServiceManager window is moved out of the main window, it becomes an independent window (no longer part of openlp main window).

Browsing the code, it looks like we have provisions for internal drag/drop (i.e.; song library to attached service manager), but do not have a provision for drag/drop to external window (i.e., song library to detached service manager).