This makes all ff_draw_* based filters aware of YUV colorspaces and
ranges. Needed for YUVJ removal. Also fixes a bug where e.g. vf_pad
would generate a limited range background even after conversion to
full-scale grayscale.

The FATE changes were a consequence of the aforementioned bugfix - the
gray scale files are output as full range (due to conversion by
libswscale, which hard-codes gray = full), and appropriately tagged as
such, but before this change the padded version incorrectly used
a limited range (16) black background for these formats.