Implement content manageable footer links


**Acceptance criteria**
- [ ] Design matches [mocks](https://xd.adobe.com/view/14ff4194-7f57-4617-5635-183575ff6d9d-62ce/)
- [ ] This page is accessed by new nav node "Footer" in the left nav (last in the list).
- [ ] Ability to add footer links
- [ ] User can user a page picker to select footer links
- [ ] Display all pages in page picker
- [ ] Adding a link will publish out the link at the bottom of the footer (site-wide)
- [ ] By default, if author doesn't add a link name, the page name will appear in the footer
- [ ] When using the website in English, the link pulls in the English title
- [ ] When using the website in Spanish, the link pulls in the Spanish title
- [ ] Alternate title: Author can optionally add a "Alternate title" to display in the footer of Janis (for example, the page [Privacy policy for Austin.gov](https://alpha.austin.gov/en/privacy-policy/) will appear as a shortened "Privacy policy" if that link name is specific in this field in Joplin). This field is should be translatable.
- [ ] Arrows allow user to change the order that the links display from left to right (the topmost link in Joplin will display leftmost in Janis)
- [ ] Limit to six; after six links are added, the "add link" button will no longer display.
- [ ] Ability to manage social media
- [ ] Authors have options to add social media links for:
- [ ] Facebook
- [ ] Instagram
- [ ] Linkedin
- [ ] Twitter
- [ ] YouTube
- [ ] When an author deselects a social media link (via checkbox) and publishes page, the social media icon and hyperlink are removed from Janis.
- [ ] Unit tests: Will we need to write any unit tests for this content type or feature set?

Start with the linked Adobe XD mock and the acceptance criteria for the new Footer navigation node, page picker, footer links, and social media settings. Done means the specified link ordering, six-link limit, translated titles, social media removal, Janis output, and unit-test decision are addressed.

Written by the indexing model from the issue text.