Assigning nodes to libraries

[MichaelMauderer]

General Summary

There should be an option in the node's context menu (RMB) to assign this node to a library. After doing so:

* The node's source code should be automatically refactored to the library's source code.
* In case the refactoring could not happen, an error with a clean explanation should appear.
* All imports in this project should be auto-refactored too. For now, we do not care about imports in other projects.

Value

First step to be able to publish a library.

Specification

• Expose the refactor functionality from the language server (Library Related API Design for the Language Server #1764) through the controller to the graph editor. Consider the best architecture for exposing similar actions in the future.
• Add an action to the context menu (Language Server does not send updates if panicing expression is changed to another panic. #1506) that refactors the currently selected nodes into a new library as per the description above.

Acceptance Criteria & Test Cases

• Working test scenario or example.
• If possible, integration tests with the language server checking for correct results.