Slurm plugin job submission info

[matthew-kusz]

This PR adds text to the Slurm plugin telling users what options they need to include when submitting Slurm jobs. More details and some examples can be found in #572, minus the linked resources appearing, and takes care of #372. There are three new env variables added:

1. SLURM_SUBMISSION_INFO - What options should be displayed
2. SLURM_DISPLAY_SHORT_OPTION_NAMES - If the short names for the options should be displayed
3. SLURM_SHORT_OPTION_NAMES - The short name for each option. If an option doesn't have a short name given here then its full name will be used

We only require the Slurm account from ColdFront when a user submits a job, so I relied on the test data for the cgray user to figure out how to show additional options.