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

Fixes #179

Implements #147

Implements #120

Implements #119

stagingType has to be non-null for the index to actually do anything (https://www.sqlite.org/lang_createindex.html -- NULL values are always considered unique)

Imported Dns rules shouldn't be deleted/inserted instantly. Instead a staging type is now used which tracks whether the rule should be deleted at the end or if the job is aborted

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