Add support for hdr metadata

The metadata we are talking about here is sometimes known as MDCV - mastering display color volume. It is a way to provide rough information about the actual color volume of content that is provided in a big color space, such as bt2100. It is provided in the same form in which color state volumes are provided too: primaries + whitepoint.

We can get this information from the content producers (recent png has chunks for it, gstreamer will have it too).

We can also get information about the target color volume of the monitor we are displaying on, via the Wayland color management protocol.

Both of these pieces can then be used to perform tone mapping (by mapping the mdcv of the content into the target cv of the monitor).