Allow exclusion of field types in Document Type Editor

Use case: The Selections plugin installs a few field types, such as System:DynamicDropdown and selection:RadioGroup. These field types can only be made working through the Console, and recently through Essentials. As Essentials is the way to add these fields, and because you can't get them to work using the current functionality of the CMS Document Type Editor alone, showing these field types as options in the doc type editor is misleading and confusing.

Currently, there appears to be no way to mark a field type as "unavailable in the doc type editor" without also rendering it nonfunctional in the document editor. So, while the doc type editor is not capable of making these fields work, it should provide a way to exclude them from the available options.