Add styles for drd modeling

We need to add the diagram-js styles so that we can use the modeling features in the adjustment EE-plugin. However, just adding the diagram-js styles like here alters existing styling in the other viewers.

We need to do one of the following

• add the diagram-js styles namespaced to the adjustment editor plugin
• cherry-pick the styles we need for the adjustment editor plugin
• add diagram-js globally and fix the unwanted side-effects
• come up with another solution