Deprecate ConcurrentHashSet in favor of Collections.newSetFromMap().

ConcurrentHashSet seems to be a relict from earlier Java times.

Since Java 1.6 the preferred method to create a "ConcurrentHashSet" is to use Collections.newSetFromMap(new ConcurrentHashMap<?, ?>())

Add PluginClassLoader plugin loader isolation mechanism

fix getAuditedStartDate resetting startDate to null

Replace Arrays.asList() (with 1 arg) with Collections.singletonList().

Replace StringBuffer with StringBuilder (for performance).

Java Generics: Fix various "unchecked" compiler warnings.

Use Collections.unmodifiableCollection() instead of obsolete Immutabl…

Use integrated AWT SystemTray and TrayIcon classes instead of JDIC.

Make code more readable by using StandardCharsets.UTF_8.

- Use String.getBytes(Charset) instead of String.getBytes(String)
- Use new String(byte[], Charset) instead of new String(byte[], String)
-> Get rid of UnsupportedEncodingException.
-> Less try-catch blocks.

Prefer StringBuilder.append(char) over append(String).

JDIC is obsolete starting with JDK 1.6:
"Most of the features provided by JDIC were incorporated into the JDK starting with version 1.6. As a result, the development of JDIC has come to an end."

Delete that class, it's not needed, since Java 5 Collections Framework.

This is the more correct API and also has very minor performance benefits.

And don't use String concatenation within the append() method.

(for performance reasons)

OF-946: Help Java to find the correct Security Provider

For some reason, the default validation fails to iterate over all providers and will fail if the default
provider does not support the algorithm of the chain. To work around this issue, the code now iterates over
each provider explicitly, returning success when at least one provider validates the chain successfully.
This replaces an earlier attempt to fix this issue by explicitly naming one (and just one) provider.

OF-946: Openfire should allow for more than one set of key stores.

OF-930: Overlay should allow for WEB-INF overrides.

OF-921: Reset MUC group cache for group changes

[OF-958] Avoiding DB properties when reading DB connection configuration

OF-959: Fixes incorrect database version.

OF-957: Audit Manager Module should be referenced by the correct name.

Improves GroupAwareMap and GroupAwareList implementations by caching
group names (in lieu of group instances) that are referenced in the
corresponding collection. This enables rapid group retrieval from
primary cache where applicable.

Adjust texts for Openfire Meetings vs Jitsi Meet

Adding some inline user documentation