vf_colorspace: Allow overriding input color properties

The filter needs input frames with color properties filled out by
the decoder. Since this is not always possible, add input options to
the filter so that user may override color space, color primaries,
transfer characteristics, and color range, as well as a generic option
to set all properties at once.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>