Add support for modeler API

Problem/Motivation

ECA 3 will no longer provide all the UI components in the eca_ui submodule, that's delegated to the new Modeler API → module which handles all the routes as well as the back and forth between ECA and the available modelers.

Proposed resolution

It would be great if this modeler would support this as well. I'd be happy to discuss with the maintainers how that would be working.

An extra benefit would then be, that this modeler would also be available for other use cases that integrate with the Modeler API, and also, ECA models could then be opened in any of the available modelers back and forth. That way, users could open a model in different modelers at different times, depending upon their needs and other context.