simplify colors

[thomcsmits]

this PR adds a prop simplifyColor. When set to true, it will take an approximate color name (from a default list, calculated in RBG space) rather than the most exact with the hex-color-to-color-name package

[thomcsmits]

@sehilyi right now a prop. Thoughts on:

1. making this the default?
2. removing the option for hex-to-color-name altogether?

[sehilyi]

I really like the change you made!

I think the simplified color names are more usable than the previous ones. More understandable and more transparent in terms of how color names are defined. I think it makes sense to at least make these the default color names. I think we can even remove the previous ones.

If we want a user to define their own color names, we can expose a corresponding function:

import { GetColorName } from 'color-hex-to-color-name';
// ...
<AltGoslingComponent
  spec={spec}
  // user can define their own color names
  customColorNames={(hex: string) => GetColorName(hex)}
/>

[thomcsmits]

@sehilyi great suggestion! merging this right now so we can use it in geranium, but I parked the customColorNames in this issue #63 to work on this in the near future