Refactoring and refinement of the `nonpublishable` attribute; facilitates DDR-1955.
Defaults the nonpublishable
attribute to false
(i.e., not nonpublishable) and defines the nonpublishable
attribute
only on resource classes that can be published (Collections, Items, and Components), since it is essentially irrelevant
to resource classes that can never be published (at least in the current code; i.e., Attachments and Targets).