``JsonViewer`` displays a JSON file in a ``QTreeView``. Internally, it loads
the contents of a file into a data structure via a string and uses it to
populate a custom tree model with JsonItemModel.

The JSON viewer demonstrates how to implement a custom item model
inherited from ``QAbstractItemModel``.

``JsonViewer`` uses the top-level objects of the document as bookmarks for
navigation. Other nodes (keys and values) can be added as additional bookmarks,
or removed from the bookmark list. A ``QLineEdit`` is used as a search field to
navigate through the JSON tree.