Store version, move main to seperate class

src/main/java/link/infra/packwiz/installer/RequiresBootstrap.java

@@ -0,0 +1,41 @@
+package link.infra.packwiz.installer;
+
+import java.util.Arrays;
+
+import javax.swing.JOptionPane;
+import javax.swing.UIManager;
+
+public class RequiresBootstrap {
+
+	public static void main(String[] args) {
+		// Very small CLI implementation, because Commons CLI complains on unexpected
+		// options
+		// Also so that Commons CLI can be excluded from the shaded JAR, as it is
+		// included in the bootstrap
+		if (Arrays.stream(args).map(str -> {
+			if (str == null) return "";
+			if (str.startsWith("--")) {
+				return str.substring(2, str.length());
+			}
+			if (str.startsWith("-")) {
+				return str.substring(1, str.length());
+			}
+			return "";
+		}).anyMatch(str -> str.equals("g") || str.equals("no-gui"))) {
+			System.out.println(
+					"This program must be run through packwiz-installer-bootstrap. Use --bootstrap-no-update to disable updating.");
+			System.exit(1);
+		} else {
+			try {
+				UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
+			} catch (Exception e) {
+				// Ignore the exceptions, just continue using the ugly L&F
+			}
+			JOptionPane.showMessageDialog(null,
+					"This program must be run through packwiz-installer-bootstrap. Use --bootstrap-no-update to disable updating.",
+					"packwiz-installer", JOptionPane.ERROR_MESSAGE);
+			System.exit(1);
+		}
+	}
+
+}