Implemented QSV encode

Major updates on AVQt::EncoderQSV:
 - Locks on a source as soon it gets initialized and unlocks after cleanup to prevent issues with multiple frame formats and HW contexts
 - Initializes and cleans up packet sinks on registration/removal if it is running
 - Stores and passes through framerate, because QSV doesn't support VFR, use VAAPI instead for this feature
 - Supports zero-copy encode when input are QSV HW frames

Minor updates:
  - Added libva to link_libraries in CMake config
  - Player example is using the static library instead of the dynamic one
  - Encoding is now enabled by default in example Player

Issue #8 is not solved by this as it only implements QSV encoding

See merge request sdcieo0330/LibAVQt!9

Resolve "Add support for zero-copy rendering to ``AVQt::OpenGLRenderer``"

Closes #6

See merge request sdcieo0330/LibAVQt!5

This reverts commit 9c357e1f

Adapted AVQt::OpenGLRenderer to use property m_position instead of local variable to prepare for implementing sync with AVQt::OpenALAudioOutput

 - simply mapping QSV frames to VAAPI and use the existing render code

TODO:
 - Code cleanup

 - Solved stretched video by setting glViewport to correctly scaled values
 - Code cleanup required
 - Running on X11 crashes with error: "Invalid EGL display"

 - Muxer: output format
 - Encoders: codec and bitrate

Further changes:
 - Added ``AVHWDeviceContext`` parameter to ``IFrameSink::onFrame()`` to prepare zero-copy implementation for encoders

 - Thanks to

 - Increased buffer size of AVIOContext in AVQt::Demuxer
 - Fixed bug in AVQt::Demuxer::init(): Allocation has to be made with av_malloc()
 - Removed include of experimental C++ headers in Muxer.cpp (Not required any more)
 - Fixed thread safe calls of GUI related functions in AVQt::OpenGLRenderer
 - Added Windows related sections to CMake files (Passing Libav and OpenAL locations with commandline arguments instead of hardcoding them)
 - Adapted example main.cpp to current state of Windows support

Finished MMAL decoder

See merge request sdcieo0330/LibAVQt!3

 - Cleaned up OpenGL code
 - Merged OpenGL and OpenGL ES shaders
 - Fixed rendering on OpenGL ES devices