Import / export of configuration for the JS client

[atooni]

This is to create an import / export facility for the configuration of displayed diagrams within the developer client.

The work is dependent on #318 and would involve.

• defining a serialization format for the configuration
• creating a form / dialog for exporting the configuration, in the first step we could just create a large text area, display the serialized config along with a copy and/or Save as... button
• creating a form for importing the configuration. Again, in the first step we could reuse the form and simply copy / paste the new configuration into the text area and confirm the change.
• letting the renderer pick up the modified configuration and display the diagrams accordingly