See also #516
The descriptive text we have is useful but it is showing up on every page due to the association with the Thing type. This makes the site less usable than before. We should slim the text down, by moving material into mainEntity and/or another document.
Moved text into datamodel doc from mainEntityOfPage.
Removed bulky text from mainEntityOfPage, and linked to it.
This saves it appearing in every single page, since it is associated with Thing.