Replace moving-color-bars pattern with smpte100, and change
moving-speed to horizontal-speed.  Default is now 0.  Add
a rotation stage to pattern building.
Allocate a temporary scanline for building images.  Remove
unused code.  Disable several patterns that we're unable to
test and probably never used.  Add other variants of bayer
sampling.  Convert some patterns to use videotestsrc_blend_line.