Items Inherit Unit- and Collection-level Staff and Special Access Roles

[joncameron]

Inherit Staff Roles and Special Access from unit/collection at the item level (instead of storing them all at the item level); includes display of default value for Special Access from collection and allows adding more at the item level.

• "Assign special access" reparented to not be under "Set Default Access for New Items"
• special access at the collection level automatically applies to items in the collection
• inheritance is additive but not allowed to be subtractive (no removing users from an item who have access set at the parent level)
• Change display of "special access" form for media object edit pages