Update assets and refactor color schemes

[adamjcampbell]

Summary of Changes

• Adds new mint colour variants
• Refactors colour variants to make use of a ColorScheme and a ColorPalette
• Moves files into a more cohesive file structure

Items of Note

File structure

Mint badge

[Rypac]

This is really good. I love what you're done with the ColorScheme enum.

Good luck integrating it with Storyboards though… 😬

[Rypac]

I'm wondering whether this name could be a little more descriptive of its intended use case. Possibly something like DynamicSVG to reflect the dynamic colour terminology of iOS 13?

Suggested change

	struct SVGPair {
	let lightSVG: SVG
	let darkSVG: SVG
	}
	struct DynamicSVG {
	let light: SVG
	let dark: SVG
	}

[Rypac]

This is great!