video, options: implement better YUV->RGB conversion control

video, options: implement better YUV->RGB conversion control

Rewrite control of the colorspace and input/output level parameters
used in YUV-RGB conversions, replacing VO-specific suboptions with new
common options and adding configuration support to more cases.

Add new option --colormatrix which selects the colorspace the original
video is assumed to have in YUV->RGB conversions. The default
behavior changes from assuming BT.601 to colorspace autoselection
between BT.601 and BT.709 using a simple heuristic based on video
size. Add new options --colormatrix-input-range and
--colormatrix-output-range which select input YUV and output RGB range.
Disable the previously existing VO-specific colorspace and level
conversion suboptions in vo_gl and vo_vdpau. Remove the
"yuv_colorspace" property and replace it with one named "colormatrix"
and semantics matching the new option. Add new properties matching the
options for level conversion.

Colorspace selection is currently supported by vo_gl, vo_vdpau, vo_xv
and vf_scale, and all can change it at runtime (previously only
vo_vdpau and vo_xv could). vo_vdpau now uses the same conversion
matrix generation as vo_gl instead of libvdpau functionality; the main
functional difference is that the "contrast" equalizer control behaves
somewhat differently (it scales the Y component around 1/2 instead of
around 0, so that contrast 0 makes the image gray rather than black).
vo_xv does not support level conversion. vf_scale supports range
setting for input, but always outputs full-range RGB.

The value of the slave properties is the policy setting used for
conversions. This means they can be set to any value regardless of
whether the current VO supports that value or whether there currently
even is any video. Possibly separate properties could be added to
query the conversion actually used at the moment, if any.

Because the colorspace and level settings are now set with a single
VF/VO control call, the return value of that is no longer used to
signal whether all the settings are actually supported. Instead code
should set all the details it can support, and ignore the rest. The
core will use GET_YUV_COLORSPACE to check which colorspace details
have been set and which not. In other words, the return value for
SET_YUV_COLORSPACE only signals whether any kind of YUV colorspace
conversion handling exists at all, and VOs have to take care to return
the actual state with GET_YUV_COLORSPACE instead.

To be changed in later commits: add missing option documentation.