changes UI to a global singleton

scenes/ui/main_menu.gd

@@ -0,0 +1,33 @@
+extends Control
+
+signal on_new_game_started
+signal on_game_continued
+
+# On ready, check which buttons to show
+func _ready() -> void:
+	if SaveGame.savegame_exists():
+		%ContinueGameButton.visible = true
+		%NewGameButton.visible = false
+
+func _on_new_game_button_pressed() -> void:
+	# Hide the main menu
+	self.visible = false
+	
+	# emit the new game signal
+	on_new_game_started.emit()
+
+func _on_continue_game_button_pressed() -> void:
+	# Hide the main menu
+	self.visible = false
+	
+	# emit the continue game signal
+	on_game_continued.emit()
+
+func _on_options_button_pressed() -> void:
+	print("TODO")
+
+func _on_licenses_button_pressed() -> void:
+	print("TODO")
+
+func _on_exit_button_pressed() -> void:
+	get_tree().quit()