LP# 1337550 Remove AggregateOffer schema.org instance

As our record details page lists each copy as a separate Offer (well, in
many cases anyway, unless paging gets invoked), the AggregateOffer
entity is not really necessary--and using it on the same page as
separate Offer entities is not recommended by at least one search engine
(per Google https://support.google.com/webmasters/answer/146750?hl=en
says a given page should include "_one_ of the following: Offer or
Offer-aggregate").

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>
LP# 1337550 remove schema.org itemOffered, add price property

We use the "offers" property to link the Product to the Offer, so there
is no reason to use a reciprocal "itemOffered" property to link back to
the Product from the Offer. The circular reference confuses some tools
(http://rdfa.info/play) and may complicate general processing, so let's
simply remove it.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>