WORK IN PROGRESS: Support offline KSK presigning

Work in progress, needs:
* review
* test case

I added logging in some places:

    if (kskOffline) DLOG(L<<Logger::Warning<<"TTL from backend DNSKEY record in '"<<p->qdomain<<"' didn't match SOA default TTL, fixing"<<endl);

Maybe this is a bad idea, as it will trigger on every query on a broken zone.. is there a better way?