libobs/media-io: Add colorspace to video info

This is useful for keeping track of what the current colorspace/range is
if a YUV format is being used.
(API Change) Add colorspace info to obs_video_info

This was an important change because we were originally using an
hard-coded 709/partial range color matrix for the output, which was
causing problems for people wanting to use different formats or color
spaces.  This will now automatically generate the color matrix depending
on the format, color space, and range, or use an identity matrix if the
video format is RGB instead of YUV.
obs-x264: Set x264 to use the cur. set cs/range

This causes x264 to use the currently set color space and color range
of the video media.  This helps prevent issues with decoding where the
colors wouldn't look right due to the fact that these settings were
never specified to x264, and prevents darkness and brightness from
looking washed out due to a potentially incorrect color range.