Use Transferable to avoid copying

[wmertens]

https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers#Passing_data_by_transferring_ownership_(transferable_objects)

Since this is meant for message passing, it should be ok that the sender no longer has the message after sending.

However, if using this for flux/redux (the whole store layer runs in a webworker), that means that the state object(s) need to be copied because the view layer needs to read it, and the actions also need acces to the state. Therefore transferable use should be optional per message…