[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