* CatalogManager.cs: Let the catalog manager ensure all command form
are instancied
* PhysicalProduct.cs: A better ToString method
* SaleForm.cs: doc
* NpgsqlContentProvider.cs: registers a command
* FrontOfficeApiController.cs: Set the catalog referer uri in each
command form found in the catalog
* FrontOfficeController.cs: creates the catalog with referer uri
* instdbws.sql: the command has got a client, as registered user
* Commande.cs: The command has an id and a product reference
* IContentProvider.cs: new RegisterCommand method
* WorkFlowManager.cs: yavscModel/WorkFlow/IContentProvider.cs
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