cubicweb #2813156 Use UUID for LDAP imports [in-progress]

Use a unique identifier instead of the DN to identify LDAP users/groups to import with ldapfeed

e.g. the entryUUID described in RFC4530: http://www.ietf.org/rfc/rfc4530.txt

priorityimportant
typeenhancement
done in<not specified>
load3.000
load left3.000
closed by<not specified>
patch[ldapfeed] Use the entryUUID attribute as extid, not the dn [rejected]