javax.annotation.Priority alternative to @Order

This commit rationalizes the use of @Order so that the standard
@Priority annotation can be used instead. The handling of both
annotations are now defined in OrderUtils.

This also updates the link to the JavaEE API so that we refer to
JavaEE7 instead of JavaEE6.

Issue: SPR-11639
Fix cache decoration

Prior to this commit, a cache that is added on-the-fly is not properly
decorated by the provided CacheManager implementation that supports
it (EhCache and JCache).

This commits adds an extra getMissingCache method to
the AbstractCacheManager that can be extended to provide a cache that
may exist in the native cache manager but is not yet known by the
spring abstraction.

Issue: SPR-11518
Fix <websocket:interceptors> default configuration

Adding a ChannelInterceptor does not suppress default executor
settings anymore in the XML namespace.

Issue: SPR-11623
Fix issue with default executor for broker channel

The default for the broker channel should be "no executor".

Issue: SPR-11623
Merge pull request #503 from sdeleuze/SPR-11623
Make WebSocket fields available after it is closed

Update some native WebSocket session getters to return basic
information after it is closed. It is required for example in
SubProtocolWebSocketHandler#afterConnectionEstablished() or
StompSubProtocolHandler#afterSessionStarted().

Issue: SPR-11621
Update JettyWebSocketSession

Ensure the JettyWebSocket session can return the Principal and accepted
WebSocket sub-protocol even after the session is closed.

Issue: SPR-11621
Move tests to packages where they belong
Merge pull request #505 from sdeleuze/SPR-11621
Fix failing test