Fix dependencies

In order to join the Spring Cloud release train we have to align the
dependencies and (more importantly) the dependency management strategy.
The strategy is to not put version  ids in <dependencies> (only
in <dependencyManagement>) where possible. And more importantly
we cannot use the releae train itself (creates a cycle).

This change achieves most of that (and mkae it possible for client
apps to use spring-cloud-starter-parent:Brixton.BUILD-SNAPSHOT)

Add spring-integration bom

spring-cloud-stream-codec/pom.xml

@@ -30,10 +30,12 @@
 		<dependency>
 			<groupId>org.springframework.integration</groupId>
 			<artifactId>spring-integration-core</artifactId>
+			<optional>true</optional>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-logging</artifactId>
+			<optional>true</optional>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>