Flyscan and furnace work

[tacaswell]

This shares commits with #26

This includes two sets of work that @tacaswell and @jklynch did for PDF "live" while supporting @DanOlds and users.

1. integration of the sorensen power supply to drive a furnace and the plans to run reasonably controlled thermal ramps (the code in 12-sorensen
2. reviving software flyscans to run XRD mapping. In addition to running (software) flyscans, this code also implements new-style blueky-darkframes darkframe colleciton. Writing out background subtracted files is done via https://github.com/NSLS-II-PDF/pdf-workers/blob/master/pdf_workers/dark_subtractor_tiff_worker.py .