[hooks/syncsources] use a cnx not a session

[hooks/notification] use a cnx not a session

[hooks/metadata] use a cnx not a session

[hooks/bookmark] use a cnx not a session

[hooks/workflow] use a cnx not a session

[hooks/email] use a cnx not a session

[hooks/integrity] use a cnx not a session

[hooks/security] let's use a connection, not a session

[server/sources/native] deal with connections, not sessions

[server] eschema_eid needs a connection, not a session

[repository] operations get a connection instead of a session Left extid2eid unchanged because that function scares the shit out of me.

[server/hook] operations get a connection instead of a session

[repository] Use an internal connection in register_user

avoid to internally raise 3.19 warnings

[sources] ensure we have a cnxset in undoable_transactions

[server] move security/integrity hook management away from InternalSession.__init__ and to Repository.internal_{session,cnx} instead. Lets internal_cnx avoid deprecation warnings.