Add tagging functionality to standards site

[michelle-rago]

Each standard has a structured set of fields. We would like the fields with controlled vocabularies to be available as tags. The tags should be clickable wherever they appear (e.g., teaser view, individual standards page).

The status tag should only have to be included in one place (not in the front matter and on the standard page).

The fields with controlled vocabularies are status, UX category, page section:

Status:

• Research
• Draft
• Pending
• Standard
• Withdrawn

UX category:

• Accessible to people of diverse abilities
• Consistent visual design and agency brand identity
• Content that is authoritative and easy to understand
• Information and services that are discoverable and optimized for search
• Secure by design, secure by default
• User-centered and data-driven design
• Customized and dynamic user experiences
• Mobile-first design that scales across varying device sizes

Page section: (This section doesn't appear on the standards site yet.)

• Top of page
• Navigation
• Content
• Bottom of page
• Metadata

[michelle-rago]

Related PR #104