add menu logic

app/src/main/java/gui/menu/StateMachine.java

@@ -0,0 +1,29 @@
+package gui.menu;
+
+import java.util.Stack;
+
+import imgui.ImGui;
+
+public class StateMachine {
+
+	private final Stack<BaseMenu> menus;
+
+	public StateMachine() {
+		this.menus = new Stack<>();
+	}
+
+	public void pushState(BaseMenu menu) {
+		menus.add(menu);
+	}
+
+	public void popState() {
+		menus.pop();
+	}
+
+	public void render() {
+		ImGui.begin("##Main Window");
+		menus.getLast().render();
+		ImGui.end();
+	}
+
+}