INT-4390: Fix tangles

JIRA: https://jira.spring.io/browse/INT-4390

Phase I: flow context/registration cycle

- extract interfaces
- rename implementations to `Standard...`

Phase II - dsl<->dsl.channel tangles

Move the channel specs to dsl.

Fix missing refactorings

(Not related to DSL) - rename core `event` package to `events`

- avoid collision with event module package
- fix tangle caused by `MessageGroupExpiredEvent`.

Phase III - dsl<->config.dsl

- move classes from config.dsl to dsl

(Not related to DSL) - fix many tangles caused by graph being a sub-package of support.management
 - make `graph` a top-level package

(Not related to DSL) - move `IntegrationManagementConfigurer` from
`management` to `config` - tangle between core and management
* Polishing Copyrights, diamonds, some JavaDocs and What's New

spring-integration-test/src/test/java/org/springframework/integration/test/mock/MockMessageSourceTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 the original author or authors.
+ * Copyright 2017-2018 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.
@@ -44,7 +44,7 @@ import org.springframework.integration.dsl.PollerSpec;
 import org.springframework.integration.dsl.Pollers;
 import org.springframework.integration.dsl.StandardIntegrationFlow;
 import org.springframework.integration.dsl.context.IntegrationFlowContext;
-import org.springframework.integration.dsl.context.IntegrationFlowRegistration;
+import org.springframework.integration.dsl.context.IntegrationFlowContext.IntegrationFlowRegistration;
 import org.springframework.integration.scheduling.PollerMetadata;
 import org.springframework.integration.test.context.MockIntegrationContext;
 import org.springframework.integration.test.context.SpringIntegrationTest;