INT-2822: 'requires-reply' for outbound gateways

* Add `requires-reply` attribute for all adapters outbound gateways as `true` by default
* WS-outbound-gateway is still without it, because it has its own specific attribute `ignore-empty-responses`
* Make `requires-reply` as `false` by default for `jdbc:stored-proc-outbound-gateway` inasmuch as `jdbc:stored-proc-outbound-adapter`
doesn't have ability to configure `returning-resultset`
* add parser tests for `requires-reply`

JIRA: https://jira.springsource.org/browse/INT-2822