INT-4042: Support Known Router Channels in Graph

JIRA: https://jira.spring.io/browse/INT-4042

```
...
  }, {
    "nodeId" : 24,
    "name" : "integrationGraphServerTests.Config.router.router",
    "stats" : {
       ...
      }
    },
    "componentType" : "router",
    "output" : "discards",
    "input" : "four",
    "routes" : [ "barChannel", "bazChannel" ],
    "errors" : "myErrors"
  }, {
...
    "from" : 3,
    "to" : 24,
    "type" : "input"
  }, {
    "from" : 24,
    "to" : 7,
    "type" : "output"
  }, {
    "from" : 24,
    "to" : 2,
    "type" : "error"
  }, {
    "from" : 24,
    "to" : 5,
    "type" : "route"
  }, {
    "from" : 24,
    "to" : 6,
    "type" : "route"
...
```

Add Graph Support for RecipientListRouter

The RLR is not an AMMR; it's the only router outside of that class hierarchy.

Polishing

Add Dynamically Routed-to Channels to Graph

Add ExpressionBased and Expose Expression in Graph

Polishing

Add getExpressionString() to IOS

Add ExpressionCapable; Set Primary Expression

Polishing - PR Comments

Router/Expression Docs

* Simple Java Docs polishing

spring-integration-jms/src/main/java/org/springframework/integration/jms/JmsOutboundGateway.java

@@ -217,6 +217,7 @@ public class JmsOutboundGateway extends AbstractReplyProducingMessageHandler imp
 		Assert.notNull(requestDestinationExpression, "'requestDestinationExpression' must not be null");
 		this.requestDestinationExpressionProcessor =
 				new ExpressionEvaluatingMessageProcessor<Object>(requestDestinationExpression);
+		setPrimaryExpression(requestDestinationExpression);
 	}
 
 	/**

spring-integration-jms/src/main/java/org/springframework/integration/jms/JmsSendingMessageHandler.java

@@ -70,6 +70,7 @@ public class JmsSendingMessageHandler extends AbstractMessageHandler {
 		Assert.isTrue(this.destination == null && this.destinationName == null,
 				"The 'destination', 'destinationName', and 'destinationExpression' properties are mutually exclusive.");
 		this.destinationExpressionProcessor = new ExpressionEvaluatingMessageProcessor<Object>(destinationExpression);
+		setPrimaryExpression(destinationExpression);
 	}
 
 	public void setHeaderMapper(JmsHeaderMapper headerMapper) {