organization/navigation of download textbooks page

[bdolor]

Description

When the admin page was first created, the list of books wasn't very long. It has since grown to a few hundred. In order to provide some organization, the interface should at the very least group them according to subject area similar to https://open.bccampus.ca/find-open-textbooks/

Expected behaviour

Navigation that groups textbooks according to subject area. Subject area should be pulled in/updated automatically, requiring no manual updates when new subject areas are added.

Actual behaviour

The items are displayed in an unorganized list.

Steps to reproduce the problem

visit admin page of Textbook for Pressbooks 'Download Textbooks', see the list, scroll, scroll some more, cringe.