Misc cleaning in pipeline_demo.py

- Enforce one-import-per-line rule
- use /usr/bin/env python in crunchbang
Rename pipeline_demo.py and move to a scripts dir

It's not really a demo anymore, it's a fully fledged entry point into
the pipelines. This name refects this maturity.

Also, util/ was supposed to be for code that is just for internal use by
developers, so it would be good if we moved all the rest of the stuff
out to ./scripts or wherever we end up. Maybe ./bin.
Add networkx to travis install list

scikit image now requires it
Add pillow to travis ci install configs
Add --exit-zero to flake8 so travis passes
Move flake8 to run tests