cubicweb #197665 locking strategies for concurrent edition [waiting feedback]

In order to prevent concurrent users to alter simultaneously the same resource.

Either pessimistic locking (reserve the resource for the 1rst user and prevent access to the 2nd user), or optimistic locking (reject the 2nd commit tentative). User(s) whose transaction has been rejected/rollbacked must be warned.

appeared in<not specified>
done in42.1337.0
load left2.000
closed by<not specified>