Added new icons for JOptionPane complete with their HiDPI variants

src/com/bulenkov/darcula/DarculaLaf.java

@@ -99,6 +99,10 @@ public final class DarculaLaf extends BasicLookAndFeel {
       defaults.put("CheckBoxMenuItem.checkIcon", EmptyIcon.create(16));
       defaults.put("RadioButtonMenuItem.checkIcon", EmptyIcon.create(16));
       defaults.put("InternalFrame.icon", new IconUIResource(IconLoader.getIcon("/com/bulenkov/darcula/icons/internalFrame.png")));
+      defaults.put("OptionPane.informationIcon", new IconUIResource(IconLoader.getIcon("/com/bulenkov/darcula/icons/option_pane_info.png")));
+      defaults.put("OptionPane.questionIcon", new IconUIResource(IconLoader.getIcon("/com/bulenkov/darcula/icons/option_pane_question.png")));
+      defaults.put("OptionPane.warningIcon", new IconUIResource(IconLoader.getIcon("/com/bulenkov/darcula/icons/option_pane_warning.png")));
+      defaults.put("OptionPane.errorIcon", new IconUIResource(IconLoader.getIcon("/com/bulenkov/darcula/icons/option_pane_error.png")));
       return defaults;
     }
     catch (Exception ignore) {