Suggestion: Read-only mode

[corentinguilloteau]

Right now, the node graph can always be edited by the user. I think a read-only mode could be a nice feature to have. I could for example allow nodes to be moved around while preventing the user from editing connections or removing a node.

A use case for this functionality could involve enabling users to modify the values within the nodes of a generated computation flow.

I feel like it could be related to #6 to some extent.