Refactored MessageConverterConfigurer

- Separated InboundContentTypeConvertingInterceptor and OutboundContentTypeConvertingInterceptor to isolate logic that needs to be performed by such interceptors for *inbound* and *outbound* messages.
- Documented their purpose via javadocs
- Moved InboundMessageConvertingInterceptor to TestSupportBinder (for now) to only support MessageCollector's 1.3 behavior

spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/config/StreamListenerAnnotatedMethodArgumentsTests.java

@@ -61,7 +61,7 @@ public class StreamListenerAnnotatedMethodArgumentsTests {
 		Sink sink = context.getBean(Sink.class);
 		String id = UUID.randomUUID().toString();
 		sink.input().send(MessageBuilder.withPayload("{\"foo\":\"barbar" + id + "\"}")
-				.setHeader("contentType", "application/json").setHeader("testHeader", "testValue").build());
+				.setHeader("contentType", MimeType.valueOf("application/json")).setHeader("testHeader", "testValue").build());
 		assertThat(testPojoWithAnnotatedArguments.receivedArguments).hasSize(3);
 		assertThat(testPojoWithAnnotatedArguments.receivedArguments.get(0))
 				.isInstanceOf(StreamListenerTestUtils.FooPojo.class);

spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/config/contentType/ContentTypeTests.java

@@ -25,6 +25,7 @@ import java.util.concurrent.TimeUnit;
 import com.esotericsoftware.kryo.Kryo;
 import com.esotericsoftware.kryo.io.Output;
 import com.fasterxml.jackson.databind.ObjectMapper;
+
 import org.junit.Test;
 
 import org.springframework.boot.SpringApplication;