Allow multiple users to edit/build in one workflow simultaneously

[kwiggins]

Some of us work in teams to build complex workflows, resulting in various versions that have to be stitched together. It would be amazing to have the workflow on a shared drive and have a mode where multiple users can build, review, and modify simultaneously. (This was one of the biggest sells for our company migration from Microsoft Office to Google suite). 

This would promote collaboration, learning, and more efficient and quality driven workflows.