Fix for issue #837 - Compile issue on OS X - include file Qt/qglobal.h not found

I updated two instances of the Qt/qglobal.h include in RemotePlugin.h to use QtGlobal as per the discussion in [Issue 837](https://github.com/LMMS/lmms/issues/837).

If i should include QtCore/qglobal.h instead, let me know and I can update.