Fixes: spring-projects/spring-integration#2071
* Clean up `build.gradle` for redundant excludes
* Add `javax.mail` dependency to WS module to avoid WARN about missed providers
* Refactoring for the XMPP module according changes in the latest Smack
* Polishing for the `BackToBackAdapterTests` to avoid extra wait for `null`
on the channel and some race conditions when client is closed during by the
`stop()` during publishing
Polishing `UriVariableTests` according the latest S-WS B-S
Revert excludes removal
bc4337ffa8