Refactor search queries: Introduced QSSQuery

Purpose is to seperate certain logic from SQLite and generalize it more.
Even though we only have Sqlite atm, in general the database layers
must be stupid as possible, while QSSQuery should do most of the hard work.

Fixes in Tokenizer logic.
Switched to C++17.

cli/sqlitedbservice.cpp

@@ -21,11 +21,11 @@ bool SqliteDbService::fileExistsInDatabase(QString path, qint64 mtime)
 	return query.value(0).toBool();
 }
 
-QVector<SearchResult> SqliteDbService::search(QString searchQuery)
+QVector<SearchResult> SqliteDbService::search(const QSSQuery &query)
 {
 	auto connection = dbFactory->forCurrentThread();
 	SqliteSearch searcher(connection);
-	return searcher.search(searchQuery);
+	return searcher.search(query);
 }
 
 bool SqliteDbService::fileExistsInDatabase(QString path)