Bad dev experience with edge selection and routing

[spoenemann]

Edges are selectable by default. And the default behavior when selecting an edge is to enable its editing mode, which makes explicit routing handles visible. But these are only visible if the respective element types are registered like this:

        configureModelElement(context, 'routing-point', SRoutingHandleImpl, SRoutingHandleView);
        configureModelElement(context, 'volatile-routing-point', SRoutingHandleImpl, SRoutingHandleView);
        configureModelElement(context, 'bezier-create-routing-point', SRoutingHandleImpl, SBezierCreateHandleView);
        configureModelElement(context, 'bezier-remove-routing-point', SRoutingHandleImpl, SBezierCreateHandleView);
        configureModelElement(context, 'bezier-routing-point', SRoutingHandleImpl, SBezierControlHandleView);

Otherwise strange overlapping messages are shown in the diagram:

We should find a way to improve the developer experience in this regard.

[jonah-iden]

This really irritated me alot when i first started with sprotty. I'll see if i can find a solution. Could someone assign me?