Slider view pre/post of carpetplot

[oesteban]

Generate carpets before and after preprocessing, and using something like https://zurb.com/playground/twentytwenty, allow the user to slide the window and compare both.

(note: @effigies suggested that the slide cursor should go up/down instead of left/right so as to make preprocessing effects more obvious)

[effigies]

https://github.com/NUKnightLab/juxtapose has a vertical sliding option