Add a QueueLinkedHashSet class

Change-Id: If58397d37b89c8fe6e099c47fb4d26fdc4589b49
Reviewed-on: http://gerrit.dmdirc.com/1632
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/util/QueuedLinkedHashSet.java

 public class QueuedLinkedHashSet<E> extends LinkedHashSet<E>
         implements Queue<E> {
 
+    /**
+     * A version number for this class. It should be changed whenever the class
+     * structure is changed (or anything else that would prevent serialized
+     * objects being unserialized with the new class).
+     */
+    private static final long serialVersionUID = 1;
+
     /** {@inheritDoc} */
     @Override
     public boolean offer(final E e) {