- Keeps the migrations to delete the public tables
- Updates and adds a global footer (admin configurable)
- Update the layout of homepage

Fixes #3110 #3559


## Test Steps

- [ ] Remove the public site, go to "Wagtail Admin" > "Pages", set the
"Apply Home Page" as the default page of the site. Remove the public
site page
 - [ ] Do regression of the whole site

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Co-authored-by: Wes Appler <wes@opentech.fund>