Refactor classes and names

[Kitchi]

Once the SLURM functionality from #6 is in place, we need a less general naming scheme for the classes. There will be two lower level classes, to deal with HTCondor and SLURM.

Potentially something like CondorDAG and SlurmDAG?

We can then implement some kind of higher level Dagger class that provides some unified interface into the two backends, but that will require more careful thought on how to keep things general but still do it in the best way.