Resolves "Tabbing issues"

Relates #13

Implemented a function that does the following.

1. When the overlay is open, focus goes on the 'Accept all cookies' button.
2. Once a user has tabbed off the 'More info' link focus is back on the 'Accept all cookies' button.

Screencast_from_29-09-22_13_37_42

Passing this for review.