Add author affiliation to page metadata

[mjpost]

This will close #2128.

[github-actions]

Build successful. Some useful links:

• Complete site preview: https://preview.aclanthology.org/author-affiliation
• Potential volumes of interest: W18-1, W18-2, W18-3, W18-5, W18-6, W18-7, W18-8, W18-9, W18-10, W18-11, W18-12, W18-13, W18-14, W18-15, W18-16, W18-17, W18-18, W18-19, W18-20, W18-21, W18-22, W18-23, W18-24, W18-25, W18-26, W18-27, W18-28, W18-29, W18-30, W18-31, W18-32, W18-33, W18-34, W18-35, W18-36, W18-37, W18-38, W18-39, W18-40, W18-41, W18-42, W18-43, W18-44, W18-45, W18-46, W18-47, W18-48, W18-49, W18-50, W18-51, (plus 19 more...)

This preview will be removed when the branch is merged.

[mbollmann]

Needs a refresh to regenerate the preview, but some comments based on the changed files

[mjpost]

My implementation here is incorrect. It reads in an affiliation and attaches it to an author, but affiliations change, and the affiliation is therefore more properly a part of a (paper, author, affiliation) tuple. So the implementation needs to change to allow for this.