Fix Tests SPR 4.1 Compatibility

GenericMessage.toString() changes.
INT-3492: Deprecate `@Payload` and `@Header(s)`

JIRA: https://jira.spring.io/browse/INT-3492

Since `@Paylod` and `@Header(s)` annotations are in the Spring Framework,
there is no more need to support them in Spring Integration.

Deprecate them and leave for backward compatibility.
Will be removed in future releases.

Remove deprecated Gatewa's `#method` expression evaluation context variable

Tested `gradlew clean testall` with and without changed to the tests.

INT-3492: Add `MessagingAnnotationUtils#findMassagePartAnnotation`

Move `MessagingAnnotationUtils` to the `org.springframework.integration.util` package
Fix JavaMail Dependency

`ImapMessage` has a direct dependency on `ReadableMime`. It is
not clear why this started failing only on the MJATS41 build
but changing the `mailapi` dependency to `compile` fixes it
(tested by pointing the plan to my repo).
INT-3369: Syslog Converter `asMap` Option

JIRA: https://jira.spring.io/browse/INT-3369

INT-3369: add option asMap in DefaultMessageConverter
* add test

GH-1250
Use com.sun.mail:javax.mail for ReadableMime dependency

com.sun.mail:javax.mail is already part of the Spring IO Platform,
whereas com.sun.mail:mailapi is not.
INT-3501 Fix IMAP Idle

JIRA: https://jira.spring.io/browse/INT-3501

There were several problems:

When a `Folder` is open, an activity on the `Store` opens a new
connection.

The `PingTask` called `isConnected()` on the store, creating a new
connection. The pings (NOOPs)  were performed on this connection and
therefore did NOT cancel the `IDLE`.

In any case, the `IDLE` was issued on the folder not the store and
the only way to cancel that IDLE is to cause its `waitIfIdle()` to
be invoked. Conveniently, simply calling `isOpen()` invokes that
method and cancels the IDLE.

Finally, the `SimpleMessageCountListener` unnecessarily invoked
`message.getLineCount()` when a simple `folder.isOpen()` is
sufficient.

Fixes:

1. Do not invoke `openSession` if `this.folder` is not null.
2. Change the `PingTask` to simply invoke `isOpen()`.
3. Move the `PingTask to the receiver for a more efficient algorithm
    instead of running on fixed interval. Rename it `IdleCanceler`.
4. Increase the PING timer from 10 to 120 seconds; add setters for it
    and the `reconnectionDelay`.

TODO: Namespace support for 4.1. (Not to be back ported).

Add a test IMAP server (ported from Java DSL and enhanced to simulate IDLE
with a new message arriving for the first idle period.

INT-3501 Polishing - PR Comments
INT-3504: Deprecate `AmqpHeaders`

JIRA: https://jira.spring.io/browse/INT-3504

* Deprecate `AmqpHeaders` and extend it from `org.springframework.amqp.support.AmqpHeaders` for backward compatibility
* Change AMQP dependency to `1.4.0`
* Remove usage of deprecated `spring_reply_correlation` and `spring_reply_to` AMQP headers
* Fix syslog `DefaultMessageConverter` JavaDoc

Reformat code
INT-3507 TCP - Use BufferedOutputStreams

JIRA: https://jira.spring.io/browse/INT-3507

TcpNoDelay (false) helps to buffer IOs but only after the
first write.

Use `BufferedOutputStreams` for TCP writes.

Use the socket `sendBufferSize` for the buffer size.
INT-1198: WebSockets: Server Side

JIRA: https://jira.spring.io/browse/INT-1198
INT-1198: WebSocket: Add namespace support

Polishing components according to the namespace support experience
Parser for `<server-container>` and tests