- Introduce a `SavedAnnotation` type to represent annotations which
   have definitely been saved and an associated `isSaved` function to
   test. Use this as the type for several methods which used to
   implicitly assume they were passed a saved annotation.

   Calls to `isSaved` have also been added in several places to check
   that an annotation has been saved, although this should always have
   been the case in practice.

 - Add missing annotation types to various parameters in
   `AnnotationsService`