plugin text syntaxes: various improvments: - syntaxes and default_syntax are now class attribute instead of members of params_data - removed local exception UnknownSyntax in favor of exceptions.NotFound - syntaxes are now saved with a key which is name in lower case and stripped, unmodified name is put in syntax's data - new getSyntax (syntaxGet in bridge) method to get syntax key and raise an error if not found. Can be used by frontends to check that a syntax is known.