[migraction] do not access session.data directly use set_shared_data and get_shared_data instead

[connection] move relation management method

[connection] give access to shared data method A reference to session data are kept

[connection] move relation cache method to Connection needed for execute (and need execute themself...)

[connection] give access to session execute from connection This allows multiple function that both requires an execute method and are required by the execute method.

[connection] move last part of undo logic in connection Now that Connection have a reference to the repo it can handle all of it itself

[connection] initialize connection.user and connection.lang A RequestSessionBase need a user and lang. For now we use the session ones. Later the Connection will have it's own.

[Connection] inherit from RequestSessionBase This contains a lot method. We need them to move more code from Session to connection.

[multi-sources] drop multi-sources related test. another branch is removing the multi-source itself. We do not want to bother fixing those test.

Use new repoapi for the web stack The publisher now link repoapi.ClientConnection to request. and explicitly control there scope. Web side, appobject._cw.cnx is now a repoapi.ClientConnection. This actually kill webonly possibility until the repoapi is able to use some RPC. The change in the authentication stack is very hasty and need cleanup