JCR copy should handle external nodes

The JCR copy operation results in a new subtree (in the same or different workspace) with new identifiers. There are three possibilities with regards to federated content:

• The source content includes federated nodes, but the target is not federated. This is essentially copying external content into the repository, and it would be nice to support this. A simple example: copy a small nt:folder and its content from a particular commit in a Git repository into the repository.

• The source content does not include federated nodes, but the target location itself is federated. This is essentially copying into an external source. Clearly the connector would have to support this, but otherwise this makes sense. Real use case: copy an internal nt:folder onto the file system via the file system connector.

• The source is federated, and the target is federated. This is either copying within a single source, or copying across sources. In this case of single source, this is something that should be handled if the connector is writable. In the case of 2 different sources, we should only allow this if both sources are the same (have the same type). Otherwise an exception should be thrown.