Logical order of custom nodes in workflows

[loleg]

As a user working with custom nodes, it would seem logical to me that the transformation in the workflow editor should happen before the template is applied. However, the documentation examples clearly show that custom nodes need to go at the end of the workflow. And when we change the order in Proxeus right now, indeed the node output is no longer available.

More problematic, and likely linked to this, the output of a custom node is not immediately visible in the document preview. One has to go back to the Documents list and open it again to see the new data.

We need to go through the sequence of frontend-backend interactions (inspect the next call in the Network devtools) and see at exactly which point transformations happen. Then we can see if it would be possible to improve this process - or at least assist the user in creating correct workflows in the UI.