Fixes/render results

[andrewljohnson]

• slim down memory usage in data pipeline until it works on my iMac and Linux boxes
  • don't make a big dict of all way bitmaps
  • batch test predictions at end of training
• add cycleway/footway args (fixes #29)
• use split reqs properly in Dockerfiles
• update README with better training image

[zain]

lgtm 👍