Optimize handling of attached objects and Tree creations

[Calamari]

I think the best way to create a Tree would be something like this:

const instance = new BTree.Instance({
  name: 'Maybe a name',
  object: { /* the object that is passed through everything */,
  tree: tree // any instance of a node 
})

This also makes it possible to register different nodes to different trees and we get rid of the awkward setObject method.