Returns a ggplot showing palettes as colour tiles with the hex value
overlaid in monospace. With palette = NULL, every palette shipped
in .ct_palettes is shown faceted.
Examples
p_all <- ct_palette_show()
p_one <- ct_palette_show("strategy_emerald")
p_vec <- ct_palette_show(c("#0F4D38", "#177B57", "#3DA876"))