Initially, I added a connection type 'admin' that was somewhat abstract. This
poses a practical issue: there's no instantiating an abstract type. As it is
hardly used, it should be removed.

This commit adds ConnectionListener and -Configuration for the webadmin panel.
This required some properties to be optional (where they were not).

This commit (which is compilable, but breaks some important
functionality - work in progess) aims to centralize the configuration
for connections. "Connections" are used in a broad sense here, and
includes socket-based (TLS and legacy-mode SSL) client connections,
BOSH-based client connections, component connections, connectionmanager
(multiplexer) connections, but also connections to the admin panel.

SSLConfig can now be used to get a consistently configured Jetty SSL configuration.

This commit:
- Refactors SSL-related code to reduce complexity and deprecate unused code
- Adds factory methods to obtain SSL/TLS engine / contexts, to replace all
  code duplication that was going on before.

The existing version of BouncyCastle (1.51) presents an issue where while working with more than
one security provider, the BouncyCastle-issued one won't be considered by the JVM. Version 1.53
does not have this problem.

Two out of three arguments in the constructor of the Server Trust Manager
are unused. By deprecating them, calling code can be simplified.

The code to get an instance of SSLContext is duplicated all over the codebase. Code gets more
maintainable by replacing all duplicate code blocks with one utility method.
This already fixes an issue where Clearspace integration used a SSL instead of TLS algorithm.

Update REST API plugin to 1.2.1

Fixed an cluster issue by create a chat room

Extended the github readme

OF-115 Process S2S stanzas from a session serially

Update web.xml schema namespaces to version 3.1 (Java EE 7)

Simplify/improve NIOConnection.deliver() by removing ByteBufferWriter.

For every packet being delivered the `ByteBufferWriter` creates a new String for every few chars written and puts it to the buffer.

According to my tests it is more efficient to create only one string and put it into the buffer once.
(10-20% better performance)

Old version 2.4 was J2EE 1.4

Also remove <taglib> from web.xml. This was required in JSP 1.2, but is no longer in JSP 2.0 (Servlet API 2.4) and gives warnings since it has been removed from the XSD.
See http://wiki.metawerx.net/wiki/RemovingTaglibFromWeb.xml

This patch removes the thread pool from the ServerSocketReader, causing
stanzas from a particular S2S session to be processed serially on the same
thread used by the ServerSocketReader.

Each ServerSocketReader currently has a thread to itself, so this is unlikely
to have a serious impact on performance, but does have a very positive impact
on correctness.

Archive legacy sources for Jive tools

These sources were added to support the pending Maven refactor (PR
#361). However the classes are not needed for the core compile/build.
Moved into separate archive for safekeeping.

The new Version.java comparison in master branch evaluates '3.11.0' as newer than '3.11.0 alpha' (which is correct), but causes a problem when attempting to load plugins requiring '3.11.0' on a developmental '3.11.0 alpha' release.

Modernize PluginManager internals with Java NIO.2 File API.

Generify ClusterTask interface

Support mock testing

OF-974: Migrate cache content

Add Legacy Jive build code for eventual removal

When switch to/from clustered deployment, ensure that critical cached
items such as components and remote servers are not inadvertently
dropped from the cache.

By replacing Jetty 6.x era libraries with 9.x-based variants, JSP support
will be brought back up-to-date. Additionally, Openfire will no longer
have a mix of dependencies from various versions of Jetty. This commit
contains a number of changes that go hand-in-hand:
- Replaces JAR files
- Applies uniformity to the buildscript where JSPC is executed
- Replaces JSTL 1.0 taglibs with later versions
- Adds a simple logger to the build process (to stop it from complaining)

in the same fashion as e.g. `java.util.concurrent.Callable`

Provide public constructor

Remove "private" default constructor to enable subclasses, mock
testing,, etc.