INT-3325 Add Redis Channel Message Group Store

JIRA: https://jira.spring.io/browse/INT-3325
JIRA: https://jira.spring.io/browse/INT-1870

Optimized MGS for QueueChannel - uses a LIST for
each channel and LPUSH, RPOP.

* Also fix MutableMessage to be Serializable

INT-1870 Priority Redis Channel Message Store

Supports priorities 0-9 (+ no priority).

Priorities out of that range are treated as no priority.

Polishing - Add Marker Interfaces

* Emit a `WARN` log if a channel is used with a regular MessageGroupStore
* Allow message-store on namespace when defining a priority channel

INT-3325 Polishing; PR Comments

Fix some typos in JavaDocs and Docs
INT-3332 GlobalChannelInterceptorBeanPostProcessor

Implicit channel declaration for items downstream
of a `ChannelInterceptor` were not created.

The `BPP` eagerly fetched the interceptors during its
own creation; this caused the context initialization to fail
because the channel initializer hasn't run yet.

Defer creation of the interceptor beans until they are
actually needed.

Also, when using `@Configuration`, the channelInitializer
is no longer the first bean in the bean factory. Before
fetching the interceptors, fetch the channelInitializer
so it will create any implicit channels.

INT-3332 Use SmartLifeCycle to Apply Interceptors

Instead of using a bean post processor, the interceptor
processor now performs the channel interception when beans
in phase Integer.MIN_VALUE are started - after all beans
have been instantiated.