Improve batch/grid submission

@pgadow added great support for submitting to HTCondor batch systems in !169 (merged). Some related tasks

• add support to submit to the GRID
• improve the slurm batch support to match the functionality of the HTCondor submission (i.e. automatically write the submission script from python). Ideally this would use a common backend with a submission script writer for either HTCondor or Slurm.