Improve proofing collaboration functionality - allow editing vs. mark up and commenting

[#1]

Would like to see improved proofing functionality that allows more than just basic markup and commenting on proofs. The vision here is that it becomes truly collaborative where multiple users can documents or spreadsheets together to more quickly get to a final approved product. The edits would have an audit trail as well as email notifications when changes are made. Also consider including shadow/backup copy functionality.