[devtools] bases for instrumenting / debugging standard propagation hooks
* a class that helps writing command to check propagation, detecting standard
errors and picture the propagation as a graph
* a class to instrument sets used to configure standard propagation hooks
closes #3171980
usr/bin/cubicweb-ctl usr/bin/
usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl