Store the version of PlantCV and the start datetime as metadata when running plantcv-run-workflow

[nfahlgren]

Is your feature request related to a problem? Please describe. When running a workflow in parallel using plantcv-run-workflow, it would be useful for error checking and reproducibility to store the version of PlantCV as metadata, along with the start datetime of the run.

Another thing we could consider adding is a file hash of the workflow script so one could tell if the workflow changed relative to what was used to produce the results.