Use cookies before falling back to a unique url

[MattL019]

The current system checks for the unique URL and if one is found it will load the appropriate focus blocks.

Alongside this system, a cookie with the unique ID that's appended to the URL should be stored, and whenever the user re-visits the site without the unique URL, we should check if they have a cookie. If they have a cookie, load their previous focus blocks.

This will mean those who forget their URL/unique ID will still have a chance of retrieving their focus blocks as long as they haven't cleared their cookie cache. We will also need to add a cookie notice to the website.

[adilanchian]

@MattL019 good looks! Would you be down to implement this? If so I can put this in the next release?