Adding isbn to the guardian.config object

Only if there is one attached.
Adding isbn to the guardian.config object

Only if there is one attached.
Updated assets to go with this pull request
Merge branch 'addIsbnToReviewArticles' of https://github.com/guardian/frontend into addIsbnToReviewArticles
Merge pull request #4647 from guardian/addIsbnToReviewArticles

Adding isbn to the guardian.config object