INT-3383: Update to Smack 4.0.0

Remove the unneeded dependency to smackx (which is now the
smack-extensions artifact). If users need functionality out of
smack-extensions (typically some XEP related one) they have to add the
dependency themselves. Note that there is also smack-experimental for
experimental and draft status XEP code.

It is no longer necessary to supress Smack path warnings.

Delete custom smack-config.xml, as all it did was disabling
certain (important) SASL mechanisms. Also remove the unit test that
verified this.

Some unit tests mock ChatManager and Chat for no reason, delete
those lines.

XMPPConnection.getHost() and .getPort() are only valid after the
connection got established, due the fact that those information is
often only available after a DNS SRV lookup was performed. Remove the
lines in unit tests that verified their value.

Remove the truststorePath example in documentation, since Smack 4.0 no
longer provides support for providing a custom truststore. Instead
ConnectionConfiguration in Smack 4.0 allows to set a custom SSLContext
(which then again can provide a TrustManager that uses a custom
truststore).
You would need some kind of isolation to have two different versions of the same library loaded (like OSGi). Not sure if this is true or possible in Spring. But even if you could do it, then there is also the API change from Smack 3 to 4. How should the user/JVM decide which version to load?

That's actually what I tried to explain in my [JIRA comment](https://jira.spring.io/browse/INT-3383?focusedCommentId=103788&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-103788): I don't know how the Spring project handles these situations, as it has many release lines, other stuff and sure some policies. All I can say is that the Smack API in spring-integration and spring-ws needs to be compatible. So it's either Smack 3 for both or Smack 4. How you achieve that is up to you.
Side node: I'm not sure if those inter-dependencies are a good design, as it causes situations like we have now, but hadn't time yet to look closer at it.