[web] start a new message system based on id of message stored in session's data instead of using __message as today, which is problematic (allow message injection). Also we can have html in messages. Removed the __createdpath hack used to escape those limitation. The old system should still work though (and will probably for a while, though we should progressivly move to the new system where it's possible). Cleanup request paramaters handling on the way.

TACHES
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-- écrire objet stocke/manipule les données

-- extraire tests de chaîne de caractère

* utiliser sqlite 

* écrire fonction prend chemin en argument et renvoie contenu

* extraire tests (chaîne de caractère) de spec 

* utiliser yams pour schéma