Adding tab trapping to cookie banner

[sarah-storm]

Adds tab trapping to the current cookie banner implementation:

• Sets an option in the settings, defaults to false.
• The trapping needs to know whether or not the banner is using a toggle so that it can also tab into the toggled options. I've added this as a setting with the class names in the classnames list, but I'm not sure that this is the best way to handle this... so any suggestions are super welcome
• Moved the banner DOM element into the state because it was in use in quite a few places
• I haven't added tests since we can't emulate the keyboard?

Absolutely would be good to compare to the implementation that @Nick-StormID and roll with the best of both worlds!

[sarah-storm]

Perfect - thanks, that's a much better way to handle the toggling! I'll be able to bring the project back in line with the package this week!