Various pipeline improvements

I've made various changes to the pipeline code. Kiyo may not agree with some of them!!

- Added the ability of the pipeline script to queue up a job on a PBS system (similar to drift-makeproducts etc.)
- Changed a few of the design decisions to make writing pipeline configs easier:
   * Allow inline parameters with each task (still allows param sections and keys)
   * Allow params key to be missing. Have to have a no_params section, and key just seems daft.