Description of problem:
As a project maintainer, I want to clone a project version, with or without source/target documents.

When branching for a new release, some project maintainers have to pull down the PO files from the old version in Zanata, then push POT and PO to the new version in Zanata.  For large projects, this can take a very long time. Most of this could be handled by CopyTrans instead, but CopyTrans does not preserve file-level credits, and is probably much slower than a straight clone.