expose --toOwner option to clone_stack

[djkapner]

the java copy stack client supports server-side copying from one owner to another. The --toOwner option is not exposed in render-python's clone_stack
https://github.com/saalfeldlab/render/blob/master/docs/src/site/markdown/render-ws-java-client.md#copy-stack-client

[RussTorres]

There are two parts to this -- one is a change in render which makes copying to an owner accessible over the REST API which is why our current version doesn't have this feature.

The other is adding the stack management client to render-python, which I'm pretty sure is missing.

[fcollman]

#99 now allows stack renames including changing owners.. not exactly the same functionality but related.