[Core] Add security warnings (i.e. "resolving address recently changed")

[wottpal]

To further improve security, warnings could be introduced esp. when resolving domains to addresses. A warning whenever a resolving address got recently changed (e.g. 1 day) would cover a lot of other cases, too (e.g. domain transfer & registrations).

Implementation-wise this could be considered to be done in conjunction with our indexer as we don't really want to store historical information like that on-chain.