Add QString overload for QGst::Parse::launch().
Add QString overload for QGst::Parse::launch().

shadeslayer/qtgstreamer,cyndis/qtgstreamer,nasserGanjali/QtGStreamer,shadeslayer/qtgstreamer,freedesktop-unofficial-mirror/gstreamer__qt-gstreamer,GStreamer/qt-gstreamer,tswindell/qt-gstreamer,knuesel/qt-gstreamer,comicfans/libqtgstreamer,cyndis/qtgstreamer,detrout/qt-gstreamer,GStreamer/qt-gstreamer,cyndis/qtgstreamer,comicfans/libqtgstreamer,tswindell/qt-gstreamer,freedesktop-unofficial-mirror/gstreamer__qt-gstreamer,iperry/qt-gstreamer,iperry/qt-gstreamer,GStreamer/qt-gstreamer,nasserGanjali/QtGStreamer,detrout/qt-gstreamer,nasserGanjali/QtGStreamer,dejunk/gstreamer,shadeslayer/qtgstreamer,knuesel/qt-gstreamer,comicfans/libqtgstreamer,ylatuya/qt-gstreamer,tswindell/qt-gstreamer,dejunk/gstreamer,knuesel/qt-gstreamer,dejunk/gstreamer,detrout/qt-gstreamer,ylatuya/qt-gstreamer,ylatuya/qt-gstreamer,iperry/qt-gstreamer,freedesktop-unofficial-mirror/gstreamer__qt-gstreamer