Purpose:

• Given a set of colors previously assigned
• Request to add N colors to the set
• Return new set of categorical colors

• given_colors - character vector of colors; bonus points: list of character vectors or color functions - convert color function to vector by using its color steps, same as jamba::showColors()
• n - number of new colors to add
• color_fn - function to generate new colors for testing. Default rainbowJam() or in future fibonacci_colors()

1. Create new_colors with color_fn
2. Call slot_colors() to assign given_colors to new_colors
3. If n colors are unassigned, assign them in order.
4. If fewer than n colors remain, repeat step (1) with n+1 colors.