Refactoring of Jersey REST resource classes for parent->child creation.

 - It's now possible to override the view class when creating an item, which
   allows specifying the specific scope and class. Other creation methods now delegate
   to this one and it replaces the more ad-hoc methods of creating child items in
   the resource classes.
 - Deserialization errors that result from invalid bundle data are now returned as
   JSON rather than a WebApplicationError stack trace.