Add an away button with global actions and message presets

The toolbar gains an away toggle with a drop-down: it toggles away on the
current server with no message, while the menu carries the global actions
("Set Globally Away", "Set Globally Away Status"), the saved presets and
their editor. Presets live in ~/.ts3jclient/away.properties and are
managed in a list with add/remove and double-click renaming.

Clients in the channel tree now show their away message in brackets after
the nickname instead of their primary server group.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ts3-client/swing/src/main/java/com/ts3client/ui/ServerTreePanel.java

@@ -590,11 +590,7 @@ public final class ServerTreePanel extends JScrollPane {
             } else if (obj instanceof ClientEntry) {
                 ClientEntry cl = (ClientEntry) obj;
                 String label = cl.nickname;
-                if (badgesOf(cl).isEmpty()) {
-                    // No icons (yet): fall back to naming the primary group inline.
-                    String primaryGroup = model.primaryServerGroupName(cl.serverGroupIds);
-                    if (primaryGroup != null) label += "  [" + primaryGroup + "]";
-                }
+                if (cl.away && !cl.awayMessage.isEmpty()) label += "  [" + cl.awayMessage + "]";
                 setText(label);
                 setIcon(iconFor(cl));
                 setForeground(cl.talking ? Theme.TALKING : Theme.TREE_TEXT);