add optional names to jobs

[BrianHicks]

Jobs currently just have their IDs and the first 20 characters (or so) of their commands. We should do two things to improve this:

1. allow job to take an optional name field. If we get that, we should present jobs with that field everywhere we can.
2. finalize what we want to do in the case where we don't have a name (the current solution is a little hacky.)

Those items can be one PR or two—they're at least partially separate!