OF-966 <failure> tag not closed for TLS Negotitation Failure

Use StandardCharsets.UTF_8 with Reader/Writer classes.

This is a followup for fcf665a9.

Use real Java enums for presence subscription states.

The homemade IntEnum and Enum classes feel totally weird and confusing, when having java.lang.Enum around.

This commit removes these classes.

The static constants in the RosterItem class now feel superfluous, but are kept in there, because they are referenced by a lot of other classes and JSP pages.

Use Collections.singleton() where ArrayList has only one element.

Fix PluginClassLoader load resource path issue  

Use try-with-resources statement to properly close resources.

Replace deprecated org.jivesoftware.util.Log with org.slf4j.Logger

- Not all resources were closed in finally block (see Launcher, PluginManager, UpdateManager, FaviconServlet, ...)
- Get rid of verbose finally blocks and empty catch blocks, which makes the code more readable.
- Generally, this is the more modern approach to deal with resources.

	When load plugin resource files old commit will load all resource with / path

	Like /images/WEB-INF/web.xml

	old commit is /web.xml

	should be /images/WEB-INF/web.xml

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<?, ?>())

This has performance benefits. On my machine it's nearly twice as fast.

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JDIC is obsolete starting with JDK 1.6: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