Notify humans about conflicts

**WIP - do not merge**

Retcon needs to notify humans when it finds a conflict it can't handle automatically (i.e. all of them). This branch will develop this capability.
This kind of wording can become out of date very easily. I'd try to write design documents as if they are currently implemented. Try to eliminate words like possibly, someone can complain if the design document says something *is* the way they don't want it to be.