argument parsing for sbatch scripts

[vsoch]

The scripts are getting interesting enough that the user should be able to provide actual arguments so we can be more specific. Eg.., instead of:

bash start.sh <sbatch> <container> <directory>

they should be able to do:

bash start.sh <sbatch> --image=<container> --notebook-dir=<directory>

That way, ordering doesn't matter either, and we can have more optional arguments.