Use new Render Layers feature with User Positions

[fuzyll]

What is the feature you'd like to have?
Customers continue to request something "closer to Google Docs" for Enterprise collaboration. They want to be able to see, in real-time, where others are in the binary and what they're working on. (They would also like to be able to have changes synced in real-time, too, but for a number of reasons both technical and non-technical, we still think this is not a good idea.)

A while back, we added the "User Positions" sidebar widget so users can see at a glance who else has the file open and you can use this to see where they are at (and navigate there with a double-click). Unfortunately, this is a lot more clunky than a visual indicator of where the other user is at.

As of build 4.3.6779-dev, however, we have the Render Layers feature that we can use to modify how Linear and Graph View look. We should explore using this to augment the User Positions feature and show visually where another user is. In particular, this would help people collaborating via voice because they can now "point" to things on another person's screen.