Revert "Revert "initial data model for toc cache, plus a preliminary exploratory script""

This reverts commit c7d02f6233de0dcdce8d89565b6257a23c4b9e8f.

Reenabling ToC-s.
Revert "Revert "add asynchronous toc task, full ToC pages for journals, and links from the search results""

This reverts commit d478ee22074a9ac58a31146e6e786ed2828b486d.

reenabling Journal ToC