Immutable.js devtool extension per Julien Deniau

The Immutable library is fantastic, but inspecting immutable collections in browser's Dev Tools is awkward. You only see the internal data structure, not the logical contents. For example, when inspecting the contents of an Immutable List, you'd really like to see the items in the list.

Chrome (v47+) and Firefox (116+) has support for custom "formatters". A formatter tells browser's Dev Tools how to display values in the Console, Scope list, etc. This means we can display Lists, Maps and other collections, in a much better way.