Refactor: Update default nav template

[erikjung]

Re: #23

Overview

This makes a variety of changes to the default patterns, pages, and navigation.

• A few more patterns have been added ("Elements") to better demonstrate that you can break patterns into multiple sections (aside from "Components")
• The color swatches have been placed in a new standalone page
• Metadata has been added to affect the sort order of some collections
• The navigation template has been updated with headings for each grouping, and now uses the sorting feature (https://github.com/cloudfour/drizzle-builder/pull/95) of the {{collections}} helper to control the order or collections.

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/CC @mrgerardorodriguez @saralohr @nicolemors

[tylersticka]

LGTM :+1:

[gerardo-rodriguez]

Yay! 👍