[hooks/security] Defer entity permission checks to an Operation. Some of these checks may currently happen twice within the same transaction and be costly. This should be semantically safe. If people rely on some internal transaction ordering to be allowed early (thus pass) while the condition wouldn't be met at precommit time, their application is broken. It however seems unlikely to happen in the real life (tm). Closes #2932033

What's new in CubicWeb 4.0?
============================

Deprecated Code Drops
----------------------

* The ldapuser source has been dropped. ldapfeed is the only official source
  remaining for ldap.