Refactor PubSubHeaders, StompHeaders, MessageBuilder

Rename to PubSubHeaderAccessor and StompHeaderAccessor
Move the renamed classes to support packages

Remove fromPayloadAndHeaders from MessageBuilder, just use
withPayload(..).copyHeaders(..) instead.

spring-context/src/main/java/org/springframework/messaging/support/MessageBuilder.java

@@ -93,18 +93,6 @@ public final class MessageBuilder<T> {
 		return builder;
 	}
 
-	/**
-	 * Create a builder for a new {@link Message} instance with the provided payload and
-	 * headers.
-	 *
-	 * @param payload the payload for the new message
-	 * @param headers the headers to use
-	 */
-	public static <T> MessageBuilder<T> fromPayloadAndHeaders(T payload, Map<String, Object> headers) {
-		MessageBuilder<T> builder = new MessageBuilder<T>(payload, headers);
-		return builder;
-	}
-
 	/**
 	 * Create a builder for a new {@link Message} instance with the provided payload.
 	 *