Use QT 5 Video Playback

.. If you build with QT 5 then we now use the QT video widgets
   instead of VLC for Windows and Linux

.. We still use QuickTime for Mac OS X

NOTE: On linux Gstreamer is used and therefore all the right
      codecs and backends need to be setup for this to work.
      On windows its more complicated as it depends how Qt
      was compiled, see:

         http://qt-project.org/wiki/Qt_Multimedia_Backends