Make the Movit converter use the correct color primaries.

We need to distinguish between the YUV primaries and the color space;
for instance, my camera outputs Rec. 601/525 YUV but uses Rec. 709 color
primaries. Also fix so that we read the correct full_luma flag, not
just check force_full_luma. (Again, my camera outputs this.)

Movit doesn't support all the exotic color spaces ffmpeg/libav does,
but this should cover most of the common ones.