Implement colorspace conversion for video frames

[illwieckz]

@slipher said:

_cinematic is just a buffer which is created without any data initially. If a video is playing, new data is uploaded each frame.
-- #1687 (comment)

To avoid dealing with too much topics, I decided to exclude the video topic from the scope of #1687:

• renderer: implement native sRGB support #1687

So once #1687 is merged we still have to implement proper colorspace conversion for video frames.

[illwieckz]

In fact it was easy to do so it's implemented in #1687:

• renderer: implement native sRGB support #1687