Implement local testing/debugging of job-dependent jobs

This should resolve issue #3 (closed).

A job that uses another job as input can now be tested locally. One can either test the desired job as usual lb-ap test <production> <job> and the code will run the job the test job depends on and pass the output to the test job. Alternatively if the dependent job has already been tested one can do lb-ap test <production> <job> -i <dependent_file_location> to tell the code to use that previous test output as input to avoid re-running the dependent job.

For running a job-dependent job in debug mode I couldn't figure out a clean way to automate running the dependent job so one will have to test that first (interactively or not) to obtain the output and then pass it to the job to be debugged by doing lb-ap debug <production> <job> -i <dependent_file_location>. I think it's probably preferred to only debug one job at a time rather than debug a chain of jobs all at once so I think not automating it in the same way as it is for tests is fine.

The README.MD is updated to describe this new functionality.

This is not yet functional for jobs where the output file type of the dependent job is different to the test job as that requires an update to the Dirac code so this will be implemented when possible.