logic: Fixed crashes and halting during indexing

* Fixed CPPSqliteException being thrown due to not properly destructed statement in addError
* Fixed indexer getting stuck after building caches because MessageFinishedParsing was interrupted
* removed Message::cancel() method and all related code

bug id = 105

src/lib/utility/scheduling/TaskScheduler.h

@@ -33,7 +33,7 @@ private:
 	TaskScheduler(const TaskScheduler&);
 	void operator=(const TaskScheduler&);
 
-	void updateTasks();
+	void processTasks();
 
 	virtual void handleMessage(MessageInterruptTasks* message);