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