Add an option to merge together second-level domains

[Bischnu]

It could be a nice feature to have the option to merge third-parties domains into a higher level domain, so the third-party www.example.com and ad.example.com would appear as one. It would lighten the tracking map and enhance its readability; furthermore as the same company owns every subdomains, it can track the user regardless of the third-party's subdomain.