Refactor and optimize digital carousel ref #6675

- Digital object carousel should NOT timeout now on
large fonds with many images.

- The digital object carousel will now properly limit
number of images displayed.

- Code is now much cleaner / refactored to remove duplicate
and unnecessary code.

- Code now uses raw SQL in some of the slowest parts

- AtoM will now cache ORM objects instead of constantly
rehydrating new ones in the Acl.