LP#1832897: business logic for carousels

LP#1832897: business logic for carousels

This patch adds various methods in open-ils.actor and open-ils.storage
to manipulate carousels. It also adds a server-side script,
refresh_carousels.srfsh, and an example crontab entry.

The new methods are:

* open-ils.actor.carousel.retrieve_by_org
* open-ils.actor.carousel.retrieve_manual_by_staff
* open-ils.actor.carousel.refresh
* open-ils.actor.carousel.create.from_bucket
* open-ils.storage.container.refresh_from_carousel
* open-ils.storage.carousel.refresh_all

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>