Push browser load

Okay, this is ready to merge! Feel free to review it, obviously.

The main benefit right now is that there's only one command-line option to specify (`--priority`), and all necessary info is fetched from `processing.json` and the LIMS. So as long as you get the priority value right, and the LIMS info is correct, everything else should fall into place.

Future work: Possibly auto-load non-customer samples, and one-stepify the actual loading process.