Simplify freestyle-usage component slugs

[chrisvdp]

Goals

• Simplify freestyle-usage slugs
• Provide better control for component usage snippets

To Do

• [ ] Make freestyle-usage slugs optional
• [ ] Document how adding a slug to a freestyle-usage component enables the focus feature
• [ ] Document how adding a slug to a freestyle-usage component results in a usage snippet in the style guide (and provide a component property to disable this)
• [x] Warn if duplicate slugs are detected
• [ ] Document how usage snippets work

Use Case

I want to render code, but not the snippet in some cases as it doesn’t add much to the styleguide. ie Headings, Typography, Color Palette.

[chrislopresto]

I'm thinking we should have a display property that defaults to 'toggle' but can be set to 'none' or 'off'... something like that.

[chrisvdp]

display: none would be how my brain works

[grapho]

what about using the component's built in isVisible property?

[chrislopresto]

The idea here is to provide a way to opt out of the automatic usage snippet. For example, we never want to see the usage snippets for things like the freestyle-palette component.