Language, audience and add custom attribute to filtering of books in the catalog

[johnpeterm]

Feature Description

Language, audience and add custom attribute to filtering of books in the catalog.

While we add book information, there could be check box for enabling and disabling particular data to be allowed for filtering and any custom attribute can be created and assigned for filtering book.

[SteelWagstaff]

Closing in favor of pressbooks/pressbooks-network-catalog#6