INT-3383: Update to Smack 4.0.0

JIRA: https://jira.spring.io/browse/INT-3383

The family of Message.(set|get)Properties methods has been factored out
of Smack as an extra extension. Use JivePropertiesManager as replacement.

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).
Updating dead links in the contributing.md file.

INT-3443: Fix `CONTRIBUTING.md`

JIRA: https://jira.spring.io/browse/INT-3443

Removing the hashtag link from the URL as it wasn't being recognized by the browser.
INT-3429 AMQP Publisher Confirm Config Improvement

JIRA: https://jira.spring.io/browse/INT-3429

Require a `confirm-correlation-expression` when a
`confirm-ack-channel` or `confirm-nack-channel` is
specified.
INT-3430 AMQP Outbound: Add Eager Connect

JIRA: https://jira.spring.io/browse/INT-3430

Add an option to eagerly connect to rabbit when
only using outbound endpoints. Log an ERROR
if the connection can not be established during
context initialization.

Polishing
INT-3416 Reset SMS.copyOnGet By Default

JIRA: https://jira.spring.io/browse/INT-3416

Add caution to docs about users getting a hard
reference to the group instead of a copy.
INT-3416 Reset SMS.copyOnGet By Default

JIRA: https://jira.spring.io/browse/INT-3416

Fix the `SimpleMessageStoreTests`