(#3063) Remove copy_allowed in favour of allowed_in_view. Also remove
copy_artefacts_allowed. copy_artefacts_allowed is unnecessary as it's only called if the copy type is 'full', and there's now no way that you would want to fully copy a block and not copy the artefacts inside it. Some other API tidyups have been done - default_artefact_config has been renamed to rewrite_blockinstance_config and had a method signature change to be a bit more flexible. The copyconfig field of the View object is gone too, no longer required.