Use a QVLCFrame as VLMDialog base class

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
macosx: re-write addon manager xib file to work-around a bug in IB 3.2
mediacodec: add a NULL pointer check after getting the profileLevels field

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>