This commit also adds various optimizations to the DnsQuery entity:
 - responses is not a MutableList anymore. This allows emptyList() to be used, saving memory.
 (- because of the prior point the query listener does not need to convert the responses to a MutableList from an immutable list, saving memory)
 - parsedResponses is now lazy. Before it was calculated for every row in the query log (every time it was scrolled to)
 - Added isHostBlockedByDnsServer, which makes it obsolete for the query log to calculate this flag for every row.
 - The StringListConverter now doesn't call gson for empty lists, saving time
 -

Closes #261