INT-4225: Add MessageConverters Infrastructure

JIRA: https://jira.spring.io/browse/INT-4225

* To allow flexible way to convert incoming messages for the target arguments in method invocation
add `ConfigurableCompositeMessageConverter` global bean under `ARGUMENT_RESOLVER_MESSAGE_CONVERTER_BEAN_NAME`
* Retrieve that bean for the `MessageHandlerMethodFactor` in the `MessagingMethodInvokerHelper` to enrich afterwards target `HandlerMethodArgumentResolver`s
* The `ContentTypeConversionTests` demonstrates conversion incoming JOSN `string` into the target POJO argument in the service method

*  Add `@Primary` support
* Add documentation about `@Primary` and `contentType` conversion

INT-1800: Add MTOM Support for WS

JIRA: https://jira.spring.io/browse/INT-1800

The Simple WebService Inbound and Outbound Gateways can operate with `WebServiceMessage`s directly.
This allows to create those messages manually and add attachments to them.
Or, on the other hand, process incoming messages with attachments manually.

For this purpose the `SimpleWebServiceOutboundGateway` is supplied with new `extractPayload` property.
Also the `UnmarshallingTransformer` can now process `MimeMessage` as payload to unmarshal it into object graph with attachments if that

INT-4225: Add MessageConverters infrastructure

JIRA: https://jira.spring.io/browse/INT-4225

* To allow flexible way to convert incoming messages for the target arguments in method invocation
add `ConfigurableCompositeMessageConverter` global bean under `ARGUMENT_RESOLVER_MESSAGE_CONVERTER_BEAN_NAME`
* Retrieve that bean for the `MessageHandlerMethodFactor` in the `MessagingMethodInvokerHelper` to enrich afterwards target `HandlerMethodArgumentResolver`s
* The `ContentTypeConversionTests` demonstrates conversion incoming JOSN `string` into the target POJO argument in the service method

*  Add `@Primary` support
* Add documentation about `@Primary` and `contentType` conversion

Doc Polishing

Change `@Primary` to `@Default`

Doc Polishing

spring-integration-core/src/test/java/org/springframework/integration/json/ContentTypeConversionTests.java

@@ -0,0 +1,130 @@
+/*
+ * Copyright 2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.json;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Collections;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.integration.annotation.Default;
+import org.springframework.integration.annotation.Gateway;
+import org.springframework.integration.annotation.GatewayHeader;
+import org.springframework.integration.annotation.MessagingGateway;
+import org.springframework.integration.annotation.ServiceActivator;
+import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.integration.dsl.IntegrationFlows;
+import org.springframework.integration.dsl.channel.MessageChannels;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageChannel;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.handler.annotation.Payload;
+import org.springframework.messaging.support.ChannelInterceptorAdapter;
+import org.springframework.test.context.junit4.SpringRunner;
+
+/**
+ * @author Artem Bilan
+ *
+ * @since 5.0
+ */
+@RunWith(SpringRunner.class)
+public class ContentTypeConversionTests {
+
+	@Autowired
+	private AtomicReference<Object> sendData;
+
+	@Autowired
+	private ServiceGateway serviceGateway;
+
+	@Test
+	public void testContentTypeBasedConversion() {
+		String json = "{\"firstName\":\"John\",\"lastName\":\"Doe\",\"age\":42}";
+		TestPerson testPerson = this.serviceGateway.convertJsonToPerson(json);
+
+		assertEquals(json, this.sendData.get());
+		assertEquals("John", testPerson.getFirstName());
+		assertEquals(42, testPerson.getAge());
+
+		Map<String, String> map = Collections.singletonMap("foo", "bar");
+		String result = this.serviceGateway.mapToString(map);
+		assertEquals(map.toString(), result);
+	}
+
+	@MessagingGateway
+	interface ServiceGateway {
+
+		@Gateway(headers = @GatewayHeader(name = MessageHeaders.CONTENT_TYPE, value = "application/json"))
+		TestPerson convertJsonToPerson(String jsonPerson);
+
+		String mapToString(Map<?, ?> map);
+
+	}
+
+	@Configuration
+	@EnableIntegration
+	public static class Config {
+
+		@Bean
+		public AtomicReference<Object> sendData() {
+			return new AtomicReference<>();
+		}
+
+		@Bean
+		public MessageChannel serviceChannel(final AtomicReference<Object> sendData) {
+			return MessageChannels.direct()
+					.interceptor(new ChannelInterceptorAdapter() {
+
+						@Override
+						public Message<?> preSend(Message<?> message, MessageChannel channel) {
+							sendData.set(message.getPayload());
+							return super.preSend(message, channel);
+						}
+
+					})
+					.get();
+		}
+
+		@Bean
+		public IntegrationFlow serviceFlow() {
+			return IntegrationFlows.from(ServiceGateway.class)
+					.channel("serviceChannel")
+					.handle(this)
+					.get();
+		}
+
+		@ServiceActivator
+		@Default
+		public TestPerson handleJson(TestPerson person) {
+			return person;
+		}
+
+		@ServiceActivator
+		public String handleMap(@Payload Map<?, ?> map) {
+			return map.toString();
+		}
+
+	}
+
+}