Some polish for self extracting jar

- show progress bar while unpacking.
- show error popup on any problem.

self-extracting-jar-creator/src/main/java/ui/ProgressApi.java

@@ -0,0 +1,8 @@
+package ui;
+
+public interface ProgressApi {
+
+	void worked(int amount);
+	void done();
+
+}

self-extracting-jar-creator/src/main/java/ui/ProgressBar.java

@@ -0,0 +1,74 @@
+package ui;
+
+import java.awt.BorderLayout;
+import java.util.concurrent.CompletableFuture;
+
+import javax.swing.BorderFactory;
+import javax.swing.BoundedRangeModel;
+import javax.swing.DefaultBoundedRangeModel;
+import javax.swing.JComponent;
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JProgressBar;
+import javax.swing.SwingUtilities;
+
+public class ProgressBar extends JPanel {
+
+	private JProgressBar progressBar;
+
+	public ProgressBar(BoundedRangeModel model) {
+		super(new BorderLayout());
+
+		progressBar = new JProgressBar(model);
+		progressBar.setValue(0);
+		progressBar.setStringPainted(true);
+
+		JPanel panel = new JPanel();
+		panel.add(progressBar);
+
+		add(panel, BorderLayout.CENTER);
+		setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
+	}
+	
+	public static ProgressApi create(int totalWork) {
+		BoundedRangeModel model = new DefaultBoundedRangeModel(0, 0, 0, totalWork);
+		CompletableFuture<JFrame> window = new CompletableFuture<>();
+		final ProgressApi api = new ProgressApi() {
+			
+			@Override
+			public void worked(int amount) {
+				model.setValue(model.getValue()+amount);
+			}
+
+			@Override
+			public void done() {
+				window.thenAccept(w -> SwingUtilities.invokeLater(() -> {
+					w.setVisible(false);
+					w.dispose();
+				}));
+			}
+			
+		};
+
+		SwingUtilities.invokeLater(() -> {
+			try {
+				//Create and set up the window.
+				JFrame frame = new JFrame("Unpacking...");
+				frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
+	
+				//Create and set up the content pane.
+				JComponent newContentPane = new ProgressBar(model);
+				newContentPane.setOpaque(true); //content panes must be opaque
+				frame.setContentPane(newContentPane);
+	
+				//Display the window.
+				frame.pack();
+				frame.setVisible(true);
+				window.complete(frame);
+			} catch (Throwable e) {
+				window.completeExceptionally(e);
+			}
+		});
+		return api;
+	}
+}