This class is required mostly as a workaround for an issue in Hibernate. It's obscure, but I'll try to explain.
SandBox ids are used as discriminators in workflow. SandBoxes themselves are also able to be managed in the
admin (add new sandbox, etc...) Site ids are used as discriminators in multitenant. When workflow and multitenant
are used together, both discriminators are in effect. Because sandboxes can be managed in the admin, it is required
that they have a site discriminator to be managed in the multitenant admin. This intermingling of references
ends up causing this exception at runtime during, for example, a product save:
HibernateException: Found two representations of same collection
To workaround, we use this management entity that exposes the properties seamlessly of SandBox to the admin, but
holds the site discriminator on its own table (rather than BLC_SANDBOX), which fixes the issue.