[forms] closes #2437859 - Detect and prevent concurrent edition of the same entity.
Add the timestamp of form generation to each entity's meta-information fields.
On form validation, check that no concurrent change is overwritten and raises
a ValidationError in case of concurrent change.
A nicer handling with a message and a link to the new version of the entity
would be a good thing...
usr/bin/cubicweb-ctl usr/bin/
usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl