Dynamic lookback Palette color mapping on Schedule

Because of the kdvs site glitch whereby successive shows may share the same show image, there can be unsightly same-color blocks on the schedule grid. Moreover, since we're randomly assigning colors to placeholder blocks, it's possible that two arbitrary consecutive shows will be assigned very similar colors. We can improve this by looking back at the adjacent timeslot's color, checking if the new color to be assigned is within a similarity threshold, and adjusting it if necessary.