Job Composer script selection should include an option to generate a script

[MorganRodgers]

Under certain circumstances (#310, #339) the Job Composer will suggest job script options from the selected directory. This is great. It is possible that a user may not have a job submission script in their directory. In this case we should offer a control to offer to create either a submission script for the user.

This submission script could be completely empty (i.e. touch submit.sh) or the contents of the default script, or some other template.

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