LOGBACK-826: work in progress on documentation

Other example configurations using layout remain and need the same
treatment.

changed SocketRemote address property to host

SocketAppenderBase uses 'remoteHost'.  The 'remote' suffix seems a
little redundant when configuring the property inside of a <remote>
component, so the preferred name is 'host' in SocketRemote.  However,
for consistency with SocketAppenderBase, this property can also be set
using 'remoteHost'.

removed name property from SocketRemote

The name served no real purpose, while creating potential for confusion
and additional noise in the configuration.

LOGBACK-826: added SocketRemote examples

Simple examples of configuring a ServerSocketAppender and a
corresponding SocketRemote.

Improvements to error logging in ConcurrentServerRunner

Leftover from the removal of the logging methods.

ConcurrentServerRunner was delegating logging to methods defined by a
subclass.  For subclasses defined in core, these methods were simply
delegating to methods of ContextAware.  For subclasses defined elsewhere
(in which a LoggerContext might be available) logging might be handled
differently.

The logging produced by ConcurrentServerRunner is mostly intended to be
diagnostic, so for consistency (no matter which module might contain the
subclass) logging is now handled exclusively through ContextAware.  This
implies that this diagnostic logging is available only when the
LoggerContext is configured for debugging, but at least that limitation
is now consistent across subclasses of ConcurrentServerRunner.

Handle RejectedExecutionException in ConcurrentServerRunner

When the Executor rejects an execute request for a client runner,
we summarily close the client socket to avoid a temporary resource
leak.

Cleaning up finally clauses with nested try blocks

LOGBACK-625: create new component that acts as a client for ServerSocketAppender

Needed some missing classes from logback master.

Not sure if the original author prefers the wildcard import...

SSLSocketRemote has an 'ssl' property of type SSLConfiguration.

SocketRemote is a component that connects to a remote
ServerSocketAppender and logs received events according to local
configuration.

Allows it to be reused for consistency in SocketRemote.

This class reimplements the much of the reconnect logic of the existing
SocketAppenderBase but does so by exposing an API that is easy to
integrate in a class that needs to handle automatic outbound connection
re-establishment, and in a way that is more easily tested.  This should
be adopted into SocketAppenderBase after some operational experience is
gained with it.

Dealing with IOException on Socket.close in each finally where it
appears is a pain...