Bug in RequestHandler.GetParams(): IParamConverter is not applied to values in IDictionary parameters

[twogood]

paramConverterManager.GetConverter() should be used to determine the converter for the IDIctionary values in RequestHandler.GetParams() and then paramConverter.ToString(value) should be used instead of just .ToString(). By default this is needed to convert DateTime values to ISO8601/RFC3339 date and time string. Should work at least for IDictionary without generics, and with IDictionary<string, object> and with IDictionary<string, DateTime>.