Add ability to specify a list of "allowed" crons

[lizrea]

For example, we might want to restrict users to only scheduling reports. I'm thinking a dropdown or other interface that adds all of the necessary path and job information, and shows the usage for that job.

runreport.pl is the first one I thought of and a good one to proof of concept.

[mrenvoize]

I'm considering issue #10 initially for allowing server administrators to mark different cron lines as 'readonly' and 'hidden' for example.

Then I think this becomes more of a 'set of templates' for users to create their own cron lines from. We could limit users to only adapting templated lines (thus the allow list approach) or be more or less permissive.

[lizrea]

This seems like a good approach