INT-3108: add requires-reply for s-a within chain

`<service-activator>` has had an attribute `requires-reply`,
but it wasn't available within `chain`.
Introduce new XSD type `serviceActivatorType`
and use it for root `<service-activator>` element and within `<chain>` as well.

JIRA: https://jira.springsource.org/browse/INT-3108