Restructure checklist data

[mxmason]

Unblocks some work in #940

Summary

This PR restructures checklist.json data so that each checklist category includes its own preface commentary. This allows us to loop over the checklist data to render each category in the list, resulting in a dryer template file.

Also:

• includes_checklist.njk has been renamed to _includes/checklist__task.njk.

Before

{
  "content": [
    {
      "title": "Use plain language and avoid figures of speech, idioms, and complicated metaphors.",
      "checkboxId": "use-plain-language",
      "wcag": "3.1.5 Reading Level",
      "url": "https://www.w3.org/TR/UNDERSTANDING-WCAG20/meaning-supplements.html",
      "description": "Write content at <a href='https://datayze.com/readability-analyzer.php'>an 8th grade reading level</a>."
    },
  ]
}

After

{
  "content": {
    "preface": "Content is the most important part of your site.",
    "tasks": [
      {
        "title": "Use plain language and avoid figures of speech, idioms, and complicated metaphors.",
        "checkboxId": "use-plain-language",
        "wcag": "3.1.5 Reading Level",
        "url": "https://www.w3.org/TR/UNDERSTANDING-WCAG20/meaning-supplements.html",
        "description": "Write content at <a href='https://datayze.com/readability-analyzer.php'>an 8th grade reading level</a>."
      },
    ]
  }
}

[ericwbailey]

I love how DRY this is, thank you. A couple of pieces of feedback, but big-picture this is great.

[mxmason]

@ericwbailey 👀 🔍

I've renamed the class to better describe what it does, as title case and sentence case are different. As a personal stylistic preference, I generally style my headings in sentence case, rather than title case. If you want something different for the headings in the checklist, I'm happy to use the text-transform-initial utility there instead.

[ericwbailey]

I also prefer sentence case. I think this is great, merging.

[ericwbailey]

Nice.

[SaptakS]

❤️