[NFR] Author to mark a Document "Group internal" so emails can't be sent to other recipients

[tjaeger]

In case the Description is not clear enough: Some Documents should remain internal, and "easy" ways should be limited to send it outside the Company or a Group - both intentionally or accidentally.

A author should be able to Flag a Document "Project Internal"

.1 A flagged Document only can be emailed to Members of the Project to consider: .2 Copy/Move Option for a flagged Document should not be possible .3 When creating Symbolic Links a flagged Document should not appear in the candidate List

It's obvious that this cannot prevent Data leakage completely, but today DMSF makes it easy (by a mistaken email) to send Documents outside a closed Group. Now we workaround this on the external Mailserver, but ideally that's being addressed within the DMSF itself.

[atopcu]

In my opinion, mail notification should be limited to who is have access right to this document.