OF-976 Language is not properly set in HttpSession

Language info should be in the Session, not in the Connection

Remove methods, which are both deprecated and unused.

Fix NPE when handling routing failures

Simplify and shorten pubsub message id

Update REST API plugin to 1.2.1

Avoids NPE by dropping (and optionally logging) error response stanzas
if the original packet has no sender JID.

The specification (XEP-0060) recommends generating unique message ids
within a pubsub instance to aid troubleshooting for notification
delivery issues when needed. This replaces a ridiculously long and
inefficient string concatenation with something a bit more tidy and
concise.

Fixed an cluster issue by create a chat room

Extended the github readme

OF-115 Process S2S stanzas from a session serially

I feel the language (the stream's "xml:lang" attribute) should be in the Session interface rather than the Connection (similar as the stream id), because it's unrelated to the session's transport.

The HttpSession already did that.

Otherwise the used language is not easy to retrieve, e.g. when using SessionManager to get the session and OF-208 is hard to solve.

Alternatively we can expose the Connection in the Session interface, but this approach feels wrong to me.

Also use `java.util.Locale` rather than String, because it better reflects what can be in `xml:lang` (it can also have country codes, e.g. "de-CH")

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.

Various improvements in Version class

byte[].equals() should probably be Arrays.equals()

Adding PropertyListener support to AuditManagerImpl