libtorc-audio: Remove some locking from AudioDecoder

- probably a precursor to removing all of the stream locking
libtorc-baseui: Add a callback queue to UIOpenGLWindow

- allows objects from non-UI threads to request a callback while the
main OpenGL context is current.
- NB we cannot guarantee thread safe access to the OpenGL contextf rom
other threads on linux as QT may acccess the master X connection during
the event loop.
libtorc-video: Add 'flip' tracking to VideoFrame

- certain streams are flagged as flipped vertically and some output
methods require it (OpenGL)
- move flip handling to VideoRenderer for consistent handling
libtorc-videoui: Hardare accelerated frames don't need an OpenGL FBO