Make D-Bus 'desktop-entry' hint match system filename.

"Clementine" (as returned by QCoreApplication::applicationName())
does not match the system .desktop file name (but it may match user
.desktop files, as was the case for me); Clementine won't be picked up
as an application in KDE Plasma notification settings unless it case
matches.

src/widgets/osd_x11.cpp

@@ -111,7 +111,7 @@ void OSD::ShowMessageNative(const QString& summary, const QString& message,
     hints["image_data"] = QVariant(image);
   }
 
-  hints["desktop-entry"] = QVariant(QCoreApplication::applicationName());
+  hints["desktop-entry"] = QVariant("clementine");
   hints["transient"] = QVariant(true);
 
   int id = 0;