This PR ensures that the annotation header is always shown, even if the
top-level annotation is hidden by a filter. The annotation header
contains the document target. This information is specially important in
the context of the notebook, where annotations from different documents
are displayed together.

I created a wrapper around the `AnnotationHeader` component. I couldn't
use it directly because I needed a couple of methods from the store to
mimic 100% the same behaviour as when `AnnotationHeader` is called
through `Annotation` component.