Have WCON demo.py parse both sides of the worm's contour

[MichaelCurrie]

https://github.com/openworm/open-worm-analysis-toolbox/blob/master/examples/WCON%20demo.py

[MichaelCurrie]

Note - WCON now has a native contour format. There still needs to be a conversion performed here.

openworm/tracker-commons#132

[MichaelCurrie]

Working on this at the https://github.com/openworm/open-worm-analysis-toolbox/tree/WCON-fixes branch.

Since it's been a while, I brought this feature branch up to date with master using:

git pull
git checkout WCON-fixes
git rebase master
git push -f