Convert flattened multi-level coordination JSON back to nested dict for to_python

[keller-mark]

Once flattened for the JSON representation, there is not currently a way to convert this back to a nested object/dict for link_views_by_dict / add_coordination_by_dict.When one of these functions generated the multi-level coordination configuration (or even when not), we should be able to identify that (parts of) the flattened data structure can be converted to the nested data structure. Then, VitessceConfig.to_python() output can be much more concise by using either link_views_by_dict or add_coordination_by_dict.