In ConcurrentServerRunner, after the LoggingContext is resolved,
informational and error messages logged by the server should no longer
be written to the StatusManager associated with the underlying Context
passed to the runner during configuration.

The references replaced should have been referring to the interface,
not the concrete implementation.  This is just a left over from the
rename-concrete-class/extract-interface refactoring sequence not
handled automatically by the refactoring tool.

Notice during copy and paste testing of the examples.

This is for consistency with the JDK documentation and system properties.

These edits integrate the documentation for SSLSocketAppender with
SocketAppender, taking advantage of the similarities of configuration
and examples.

This should make it easier to diagnose SSL negotiation problems, in
particular.

The DEFAULT_PORT defined in SocketAppenderBase needed a public modifier
to allow it to be referenced in SocketServer.

If the appender configuration did not specify an SSL configuration, an
NPE would occur in method start when creating the SSLContext.  This NPE
would be trapped and logged, but subsequently the getSocketFactory
method would be called and would return null, potentially causing an NPE
further up the stack.  The fix is to ensure that the appender always has
a default SSL configuration, even if one is not specified in the Joran
configuration.

Unit tests for the SSLConfiguration already validate that an SSLContext
can be successfully created from an SSLConfiguration that is merely
instantiated, but has none of its properties configured.

The SSLSocketServer now allows an "ssl" element of type
SSLConfiguration.

Modified DefaultNestedComponentRules to include rules for SocketServer.

This commit allows a SocketServer to be configured in a Joran
configuration file.

This commit includes the server class itself, along with unit tests.

This commit includes the SocketServer, supporting classes, unit tests,
and a functional test for the server itself.

This behavior is now documented for the method and validated with
a unit test.

LOGBACK-818: support for SSL-enabled socket appender and server