Spring Boot 2.1 upgrade

* Removed MockBinderRegistryConfiguration
* Move necessary beans from `BindingServiceConfiguration` which is now auto configurable into
  `BinderFactoryConfiguration` that is invoked by `EnableBinding` in order to avoid certain
  cyclic dependency issues. The beans moved are binding target factories of type
  `MessageSourceBindingTargetFactory` and `SubscribableChannelBindingTargetFactory` and their dependencies.
  As a side effect, `ContentTypeConfiguration` is also brought back at the `EnableBinding` level through
  `BinderFactoryConfiguration`.
* Restore `ServerController`  bean in SchemaServerConfiguation as the removal of it
  earlier introduced  some connectivity issues with the schema registry server.
* Update copyrights

spring-cloud-stream-schema/src/test/java/org/springframework/cloud/schema/avro/AvroMessageConverterSerializationTests.java

@@ -68,7 +68,7 @@ public class AvroMessageConverterSerializationTests {
 	@Before
 	public void setup() {
 		schemaRegistryServerContext = SpringApplication
-				.run(SchemaRegistryServerApplication.class);
+				.run(SchemaRegistryServerApplication.class, "--spring.main.allow-bean-definition-overriding=true");
 	}
 
 	@After

spring-cloud-stream-schema/src/test/java/org/springframework/cloud/schema/avro/AvroSchemaRegistryClientMessageConverterTests.java

@@ -60,7 +60,7 @@ public class AvroSchemaRegistryClientMessageConverterTests {
 	public void testSendMessage() throws Exception {
 
 		ConfigurableApplicationContext schemaRegistryServerContext = SpringApplication.run(
-				SchemaRegistryServerApplication.class);
+				SchemaRegistryServerApplication.class, "--spring.main.allow-bean-definition-overriding=true");
 
 		ConfigurableApplicationContext sourceContext = SpringApplication.run(AvroSourceApplication.class,
 				"--server.port=0",