Support importing symbols from libraries

[nilsdoehring]

Situation:
When an override points to a symbol that is only present in a library, a pull has no effect.
As soon as an instance of that symbol from the library is inserted anywhere in the Sketch file, a pull sets the override successfully.

Desired behaviour:
When an override points to a symbol that is only present in a library, a pull should set the override successfully.
This might have to do with the Sketch API expecting specific library symbol imports.

[dbrody]

We've addressed this in release v8.4.2-alpha.

[nilsdoehring]

Works like a charm, thank you so much!