Add a new rule to validate TLDs

[scripthunter7]

We already have a basic domain validator in AGTree. This is used to validate the domain list of the cosmetic rule or the value of the $domain modifier.

I recommend improving this utility by checking TLDs (if the TLD is not a wildcard, like example.*)

References:

• known TLDs (we may can import known TLDs to a Set from here)