WebSocket plugin: Fix wrong namespace adding to empty elements

The old logic produced XML like:
<presence xmlns="jabber:client" from="..." to="..."><show xmlns="">xa</show><status xmlns=""/></presence>

This is basically the same fix as in 6965c13e.

Relates to OF-938.

Remove verbose logging

OF-1009: Allow non-TLS dialback

When a TLS failure occurs during dialback, allow for a non-TLS
based fallback.

This class logged to debug on any property change (including properties
that do not relate to the class itself).

S2S logging

OF-1023: Fire contactChanged/Deleted events

OF-999: Allow configuration of BOSH worker thread pool

OF-998: Ant should resolve DTDs locally

OF-1025: Restore web-custom.xml functionality

OF-1000 Prevent NPE and improve logging

Fixed group population for colliding full names.

OF-122: MUC subject change policy

MUC Invitation rejection delegate call

For some reason, XPath-based selection of nodes no longer works. Traversing
the Dom4j object resolves that problem.

Improve quality of random data generation.

Ant (or rather, the XMLTask in our build) attempts to lookup DTDs
online. The build (of plugins) will fail if no internet connectivity
is available. This commit references DTDs locally, allowing Ant to
skip the online lookup.

When a log directory cannot be created, a warning should be logged,
and null pointers should be prevented when the directory is being
referenced.

The thread pool that performs processing of data received through the HTTP-based
connections of BOSH (as provided by Jetty) should not have a hardcoded upper bound.
Instead, the pool size should be configurable.

For other connection types, this is managed by properties named as such:
 - xmpp.client.processing.threads (client sockets)
 - xmpp.multiplex.processing.threads (connection managers)
 - xmpp.component.processing.threads (components)

BOSH does have a similar property: httpbind.client.processing.threads
It's value however is not used to configure the amount of worker threads. It is
used to configure the amount of (NIO) acceptors instead. In NIO, acceptor
threads handle network IO, and hand off processing to the worker threads.

There's little benefit in being able to configure the amount of acceptors, as
Jetty will default to a platform-specific default (based on the number of CPUs
that are available). There is greater benefit in being able to configure the
amount of worker threads (as that's more likely to affect throughput).

Per PR feedback, default to a strict (conforming) policy when detecting
MUC room subject change requests.

Additional work could be done to add a corresponding configuration
option to the MUC service admin console, but is not included in the
scope of this PR.

StreamIDFactory is designed to generate stream IDs. It's silly to use
something else when generating stream IDs.

When a shared group is removed from a roster item, fire an update or
delete event to keep the corresponding Roster cache in sync.

Stream ID generation should be based on a strong random number generator,
should use a wider variety of characters than just hexadecimals, and
could be a bit larger for reduced chance of duplicates.

Clarified the role in which Dialback is acting.

Reduced code complexity by removing code for which there is no execution path.

This commit reduced duplicated code that creates a socket to any
of the DNS-SRV-based hosts for an XMPP domain by moving that code
to a new utility class.

Additionally, S2S logging was improved: references to 'remote hosts'
where replaced by 'remote domains' to differentiate between servers
and domains (that can consist of multiple servers).

xml:lang in stream header should conform to a language tag.

toString() was called on the Locale here, resulting e.g. in "de_DE".
Instead it should be "de-DE".

Improving logging for S2S / dialback

Default to lenient policy, allowing override to strict (conforming)
policy. Tested using Pidgin, Psi, and Exodus. Refer to details in
OF-122.

Add explanation to setup about default admin password

Fix twice sending of messages on route.really-all-resources=true

The S2S (federation) code was not big on logging. This commit
introduces new logging, and structures the logged messages.
This commit does not introduce functional changes.

Add explanation to setup about default admin password
https://igniterealtime.org/issues/browse/OF-1016

When LDAP search returns a multiple result set for a user CN,
we now iterate through the entire set to find a matching user DN.

add call of sendingInvitationRejection for MUCEventDelegate

add event delegate on decline invitation