Worked on Nvidia encoder.

src/encoder/encoder.cpp

src/encoder/encoder.hpp

src/encoder/nvidia_encoder.cpp

src/encoder/nvidia_encoder.hpp

src/encoder/vulkan_encoder.cpp

src/encoder/vulkan_encoder.hpp

src/headset/emulated_headset.cpp

src/headset/remote_headset.cpp

src/vr_application.cpp