[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.