Not enforcing EnableAutoConfiguration on aggregate parent

- The aggregate parent configuration now imports the required auto configuration classes such as ChannelBindingAutoConfiguration and EndpointAutoConfiguration
while `@EnableBinding` is still at the parent configuration to be able to share the binding configuration among the child applications
 - Add `ConditionalOnMissingBean` in spring cloud stream auto configuration classes so that if `EnableAutoConfiguration` is enabled at child application classes
they don't get instantiated again
 - Conditionally import EmbeddedServlet auto-configuration when web environment is enabled for parent
 - Add test

Resolves #737

spring-cloud-stream-codec/src/main/java/org/springframework/cloud/stream/config/codec/kryo/KryoCodecAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 the original author or authors.
+ * Copyright 2015-2017 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.
@@ -51,6 +51,7 @@ public class KryoCodecAutoConfiguration {
 	KryoCodecProperties kryoCodecProperties;
 
 	@Bean
+	@ConditionalOnMissingBean(PojoCodec.class)
 	public PojoCodec codec() {
 		Map<String, KryoRegistrar> kryoRegistrarMap = applicationContext.getBeansOfType(KryoRegistrar
 				.class);
@@ -58,6 +59,7 @@ public class KryoCodecAutoConfiguration {
 	}
 
 	@Bean
+	@ConditionalOnMissingBean(KryoRegistrar.class)
 	public KryoRegistrar fileRegistrar() {
 		return new FileKryoRegistrar();
 	}