Enable configuration for the JS Client

[atooni]

We want to capture all configuration aspects of a displayed diagram within the JS client, so that we have a full description what we need to display within the page.

This would involve reactoring the current client implementation, so that

• the UI interactions to add a diagram would add another instance of the config case class to the display state of the page
• the page rendering would just rely on the collection of configured diagrams to create the current view.

[atooni]

We have now refactored the clients internal data model and have introduced a Diagramsconfig. Whenever the user decides to add a diagram, a new instance of the config is created and the diagrams section is now using a Laminar signal-split to render the diagrams

[atooni]

Rolled into #317