add click sound as SFX

scripts/MainMenu.gd

@@ -6,12 +6,15 @@ func _ready():
 	print("MainMenu ready")
 
 func _on_new_game_button_pressed():
+	AudioManager.play_ui_click()
 	print("New Game pressed")
 
 func _on_settings_button_pressed():
+	AudioManager.play_ui_click()
 	print("Settings pressed")
 	open_settings.emit()
 
 func _on_exit_button_pressed():
+	AudioManager.play_ui_click()
 	print("Exit pressed")
 	get_tree().quit()