We implemented this by allowing each library to choose which entry points are enabled: 

To disable audiobooks for a library you disable the 'Audiobooks' entry point.

If one or zero entry points are enabled, the facet group for switching between entry points is not added to the feed. When SimplyE receives a feed with no entry point facet group, it should (and presumably does) omit the UI elements that allow the user to switch between entry points.

The circulation manager knows about every item in its collections, even if some of those items are not shown in the catalogs for particular libraries. That is, disabling the "Audiobooks" entry point will not delete the audiobooks' catalog records.

n.b. after enabling or disabling an entry point, the changes will not be visible to users until the next time cache_opds_blocks is run.

Acceptance criteria:

• Current version 2.2 (without Audiobooks) of the app passes main regression tests whether Audiobooks are turned on or off