Make homepage editable in Wagtail

[csebianlander]

This PR reworks our homepage, currently hard-coded, into editable fields in Wagtail

It is currently incomplete and in very draft form as I start hacking at the existing code and trying to build some bespoke field panels for use on the home page.

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How to test this PR

1. localhost
2. View /, both in its front-end rendering and back-end forms

Notes and todos

• This will probably need to be a multi-phase rollout to ensure we don't have a period of displaying a broken/empty homepage. I'm thinking one PR with all the back-end changes but which preserves the current hard-coded html pages, and then a second PR which swaps those out for the correct template files.

Checklist

• PR has an informative and human-readable title
  • PR titles are used to generate the change log in releases; good ones make that easier to scan.
  • Consider prefixing, e.g., "Mega Menu: fix layout bug", or "Docs: Update Docker installation instructions".
• Changes are limited to a single goal (no scope creep)
• Code follows the standards laid out in the CFPB development guidelines
• Future todos are captured in comments and/or tickets
• Project documentation has been updated, potentially one or more of:
  • This repo’s docs (edit the files in the /docs folder) – for basic, close-to-the-code docs on working with this repo
  • CFGOV/platform wiki on GHE – for internal CFPB developer guidance
  • CFPB/hubcap wiki on GHE – for internal CFPB design and content guidance

Front-end testing

Browser testing

Check the current browser support cutoff list](https://cfpb.github.io/consumerfinance.gov/browser-support#current-browser-support-metrics) for browsers that are advisable
to prioritize for testing.

Accessibility

• Keyboard friendly (navigable with tab, space, enter, arrow keys, etc.)
• Screen reader friendly
• Does not introduce new errors or warnings in WAVE

Other

• Is useable without CSS
• Is useable without JS
• Does not introduce new lint warnings
• Flexible from small to large screens