Add label should be present on annotation body

[glenrobson]

Implementing this recipe:

https://iiif.io/api/cookbook/recipe/0219-using-caption-file/

Which has a label in the body. BodyItem should be added to the following list of classes:

Potential bug location(s):

iiif-prezi3/iiif_prezi3/helpers/add_label.py

Line 3 in aeed7b6

from ..skeleton import (Annotation, AnnotationPage, Canvas, Collection,