MainPage.xaml.cpp: set cvImage inside of lambda, call copyOutput() on UI thread
cap_winrt.hpp: change input buffer to Mat from WriteableBitmap
cap_winrt.cpp: protect input buffer initialization with a mutex against UI thread
cap_winrt_highgui.hpp: provide access to OpenCV input Mats using a ptr
cap_winrt_highgui.cpp: relay copyOutput buffer to Video::copyOutput()
cap_winrt_video: use bgra8 for testing, use ContiguousCopyTo into input Mat, add Video::CopyOutput()
main.cpp: set top of frame to green to simulate some image processing in OpenCV using a Mat