add hex_to_dec function to util

there for replace_template_colors
add unique_path to util (and tests)

unique path is for replace_template_colors, but it’s useful for several
places throughout the package, whenever files are output and shouldn’t
be overridden. Should at least make its way into `csv_tools`
continue on replace_template_colors

work on everything but make_color_replacements. still bugs around not
inputting things correctly, etc, but overall flow including except
replacing colors but including saving now works