Commands Refactor Part 2

We split #196 in two parts. this is the second. (#262 is the first). This builds on all the changes to commands/.
That change was part of the port, the command previously had `importer.BuildDagFromFile` and that needed to be changed to run on the daemon. It was my mistake using `NewDagFromReader` instead of `BuildDagFromReader`, although those aren't the best names since I have no idea what the difference is.