app: add a dialog popup, and a quit button

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

src/helloworld/app.py

@@ -20,20 +20,36 @@ class HelloWorld(toga.App):
         name_box.add(name_label)
         name_box.add(self.name_input)
 
-        button = toga.Button(
+        hello_button = toga.Button(
                 "Say Hello!",
                 on_press=self.say_hello,
                 style=Pack(padding=5)
                 )
+
+        quit_button = toga.Button(
+                "Quit",
+                on_press=self.quit,
+                style=Pack(padding=5)
+                )
+
         main_box.add(name_box)
-        main_box.add(button)
+        main_box.add(hello_button)
+        main_box.add(quit_button)
 
         self.main_window = toga.MainWindow(title=self.formal_name)
         self.main_window.content = main_box
         self.main_window.show()
 
+    def quit(self, widget):
+        if self.on_exit is not None:
+            self.on_exit()
+        self.exit()
+
     def say_hello(self, widget):
-        print(f"Hello, {self.name_input.value}")
+        self.main_window.info_dialog(
+                f"Hello, {self.name_input.value}",
+                "sup dawg!"
+                )
 
 
 def main():