Add support for class labeling of bbox

[ibayer]

Motivation

ipyannotator currently support single object location with a bounding box (bbox). However annotating the type / class of the object is currently not supported.

Develop and Integrate Class Labeled BBox Widget

Suggested steps:

• explore 01c_tutorial_bbox.ipynb to see the current bbox implementation in action
• extend 01_bbox_canvas.ipynb with a new class LabeledBBoxCanvas which supports displaying and drawing of a class labeled bbox.
• duplicate 04_bbox_annotator.ipynb as 04b_class_bbox_annotator.ipynb and replace the BBoxCanvas with LabeledBBoxCanvas