Finished playback control

res/gui/fragments/PageMedia.qml

res/gui/fragments/PageStreaming.qml

src/API/NetworkAPI.cpp

src/API/NetworkAPI.h

src/GUI/VideoGuiLauncher.cpp

src/GUI/VideoGuiLauncher.h

src/GUI/WindowCloseEventFilter.cpp

src/MediaProcessing/VideoTranscoder.cpp

src/MediaProcessing/VideoTranscoder.h

src/Networking/NetworkSinkHandler.cpp

src/Networking/StreamThread.cpp

src/Networking/StreamThread.h

test/main.cpp