Bug 36566: Correct eslint errors in OPAC enhanced content JS

Bug 36566: Correct eslint errors in OPAC enhanced content JS

This patch fixes various eslint errors in enhanced content JS files:

- Consistent indentation
- Remove variables which are declared but not used
- Add missing semicolons
- Add missing "var" declarations

To test, apply the patch and clear your browser cache if necessary.

- Go to Administration -> System preferences and enable these
  preferences:
  - OPACAmazonCoverImages
  - BakerTaylorEnabled
  - GoogleJackets
  - OPACLocalCoverImages
  - OpenLibraryCovers
- Go to the OPAC and confirm that covers from these services appear
  correctly in search results and on detail pages.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>