Duplicate and unpublish action, template/draft documents

[roman-yagodin]

It probably have sense to introduce combined "Duplicate and unpublish" action to allow quick copy of documents, and also introduce some kind of "template/draft" flag, so newly created copy not became published, even then it has proper start/end dates set for that.

Then we promote "template/draft" document to regular one (by removing this flag on save/update), it will be saved as new document, not inheriting original document created/last modified dates. I think this approach will play nice along with the DNN page templates.