some suggested improvements

[justin-calleja]

This PR:

• uses check_box.set_pressed_no_signal when setting the value of the check_box when we do not want to trigger a signal (instead of button_pressed which triggers a signal)
• adds settings.settings_changed.connect(_on_settings_changed) so that any changes made in Godot's UI to set this checkbox reflects in the extension's checkbox (keeps them in sync).

[cuppar]

Thank you very much for your advice, I learned a lot from it. :)

[justin-calleja]

Thank you for the plugin. It helped me get started with Godot plugin dev 🍻