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/commandsearch.cpp

@@ -25,8 +25,7 @@ int CommandSearch::handle(QStringList arguments)
 
 	QStringList files = parser.positionalArguments();
 	QString queryStrings = files.join(' ');
-
-	auto results = dbService->search(queryStrings);
+	auto results = dbService->search(QSSQuery::build(queryStrings));
 
 	for(SearchResult &result : results)
 	{