remove isValidHex validation from Swatches

[kriscarle]

This changes Swatches to be consistent with Github and Circle.

This fixes #488 and makes it up to the user to control the color values via props, letting you use hex8 or rgba in these components (if your use case supports it) since the component itself does not need to validate an end-user hex6 text input.

It could also make sense to have the onChange property of these components return a color string value instead of color.hex but that would be a breaking change to the interface. May be better for this to just be an undocumented feature for those of us that need it? Meaning that these components are "dumb" and will pass through whatever values we feed in.

[casesandberg]

This is great, thanks!