Graph Discussion (Temporary)

Since commenting directly on lines in github is easier than anything else I can think of, I'm opening this PR to pass feedback to @mtbc. I've marked it "exclude" and it will likely be closed quite soon. ~Josh.

--exclude
The design of much of `omero::cmd` is to not use Model objects so that a very small executable can be compiled which only relies on primitives. That doesn't make it a necessity, but we should be clear about a move away from that.