Collection schemas

This release introduces our new collection schema feature that provides: initial contents for new files, and a structured approach to managing content. A number of other features and fixes are also included.

Features:

• Collection-level option called schemas to define one or more types in a collection. Used for the contents of new files, and keeping existing files up to date.
• Schema-level configuration for changing the file preview in the collection file list.
• Extended options for non-default add_options.
• Default add_options in the collection file list +Add menu generated from schemas if set.
• Collection-level options for disable file actions and add folder action in collection file list.

Fixes:

• Failed payment emails now correctly state downgraded plan.
• Error handling previewing files with an unauthorized DAM.
• Transfer requests list now correctly listing all pending requests.