[request/session] refactor language handling: don't attempt to sync web/repo languages This decouple thing and make code easier to understand. Previous behaviour was fine w/ validation error that were translated on the server side, but isn't satisfying for notification and all. Now: * translations should be done on the ui side (see previous validation error refactoring) * consistent behaviour: each side (web/repo) is responsible to deal with its request/session of language, no weird interaction between them on this topic * drop on the way the 'session properties' api, used only for that matter. -> much simpler/cleaner/saner api The thing missing being a way for user to tell "My favorite language is xxx but I also want cw to consider my http language header)

[config] turn internal configuration methods building appobjects search path into normal method rather than class method as this is useless and make path filters difficult to override (we had to override the class attribute, as instance attributes were not seen). Also rename related methods for consistency with current vocabulary

fix missing import

backport stable

[hooks/syncshema] fix logging level and nicer message (wrong changeset published previously)

[hooks/syncschema] do not crash on DROP of an already dropped index/... (closes #2465393)

[cwctl] show a better diagnostic message on version violation (closes #2464800)

[tabs] fix pb with non-lazy tabs: style isn't properly set due to missing jquery.ui activation. Closes #2465657 also do a small cleanup on the way, and properly implements render_entity rather than cell_call, as one would expect regarding default PrimaryView code.

[migration] fix backward compat for rename_relation

[datafeed] make cnxset handling of datafeed source more robust currently we may run in some cases where the session has no more cnxset depending on errors and parser's handling of the cnxset. Also, free the cnxset and reacquire it later, letting a chance to other threads to run.