Update better-better-booru.user.js

All settings are saved to a single key in localStorage and stored to an object when retrieved. Storage and retrieval of the settings is done via JSON's parse and stringify methods.

* Speed should be improved due to decreased calls to localStorage on the hard drive. The object in memory will handle all changes and calls for values.
* Conversion of booleans/numbers is handled by JSON. If you set a value to a boolean, it will be retrieved as a boolean. No more need to manually convert. Having a native method handle this all at once should be faster than individually converting each value as well.
* Having the object act as a middleman between the user and saved settings allows for the saved settings to be restored in the event of the user wanting to cancel changes.

Notes about changes:
* Added a "Cancel" button that allows the user to cancel any changes they make with the panel open. This includes canceling an accidental click on the reset option.
* Changed "Reset Settings" to "Reset to Defaults" to clarify that settings were being reset to "factory defaults" and not to previously saved/unaltered settings.
* Changed "Close" to "Save & Close" to better reflect what the button does now that "Cancel" is an option.
* Grouped all the "hide notice" options together.