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 don't test SASL here, it's just a pretty useless test to see if the `PLAIN` mechanism is registered and another strange test to assure that the number of registered/known SASL mechanisms is exactly two (but there could be easily more).
I don't know the motivation behind that test, but it seemed counterproductive to me.