Programatically generate color scheme for HTML report graphs.

[slashrsm]

At the moment we're using pre-defined color scheme with limited number of colors. In cases where there will be a lot of lines on the graph we'll start seeing color repeating. It would be awesome if we could programmatically generate as many colors as needed.

More info: https://github.com/tag1consulting/goose/pull/415#discussion_r804441410