HZ-9: Ensure clustering works properly when enabled through the admin UI

OF-1495: Add subject alternative names to certs and CSRs

Depending on what components (plugins) are loaded, the certificate that is used to identify the local
domain should have additional values in its Subject Alternative Name extension.

This commit adds an information header in the TLS admin console pages when Openfire is serving components
that are not included in its certificate.

OF-1496 reduce discovery complexity

OF-1191: Use client truststores for c2s-type connections.

OF-1501: Prefer NewSunX509 KeyManager implementation.

OF-1481: Don't attempt to send over a non-existing connection.

Instead of waiting for data to become available on the main thread, this task is better offloaded to a dedicated
thread pool. This prevents worker threads from locking up (which potentially cripples the server).

This is a very basic (and inefficient, and prone to cause thread starvation) change that causes
MAM queries to be responded to only after all relevant data has become available in the database.

Prior to this commit, archived data was kept in a buffer, which was flushed to the database once per minute.
It is undesirable to have the database 'lag behind' for such an extend period of time.

This commit introduces near-instantanious flushes. Data that's put in a buffer is flushed immediately, unless
more data is available instantly.

* OF-1484: Allow admin console pages to be ordered explicitly.

* OF-1484: Admin console's "Plugins" tab should be on the right.

This commit forces the 'Plugins' tab to be the rightmost tab, even when plugins
add new tabs to the admin console.

Preserve the null modification date when serialising/deserialising

Upon External Serialization, do a nulll check on modificationDate. It is possible that the modificationDate is null, if the room was just created through REST API. That results in an NPE,
partial room creation, and failure in communicating the room updated event via hazelcast.

If modification date is null, send the creationDate value instead.
see https://discourse.igniterealtime.org/t/openfire-hazelcast-clustering-rest-api-room-creation-npe-when-no-modificaitondate-sent/80619/2

HZ-11: Fire the left cluster event before we leave the cluster

closes #1030

This invocation added data to a copy of the source material, instead of the source itself.

XMPPServer should not expose Service Discovery data providers that do not cover all service discovery information
that applies to the XMPP domain. It did so, as it only exposed providers that were based on its modules, but not
other components.

When displaying the details of a certificate, the admin console now also shows
its PEM representation. This is convenient for copy/pasting the certificate into
other tools.

OF-1494: Fix the xmppAddr SAN othername entry in generated certs.

was missed for maven builds previous to 4.2.2 release

Handling xmppAddr being a type of ASN1TaggedObject (i.e. DERTaggedObject) as it fails to cast the xmppAddr to ASN1String to work with CA signed certificates/self-signed certificates generated with OpenSSL.