Removing BacktestingTransactionHandler thread

- For backtesting the algorithm thread will sequentially process pending
order requests
   - Adding new non blocking `BusyCollection`
- Updating `UpdateOrderRegressionAlgorithm` that suffered of a race
condition: it supposed `OnOrderEvent` would be called after the call to
`Transactions.AddOrder()` was finished

Algorithm.Python/UpdateOrderRegressionAlgorithm.py

@@ -134,4 +134,4 @@ class UpdateOrderRegressionAlgorithm(QCAlgorithm):
             self.Log("FILLED:: {0} FILL PRICE:: {1}".format(self.Transactions.GetOrderById(orderEvent.OrderId), orderEvent.FillPrice))
         else:
             self.Log(orderEvent.ToString())
-            self.Log("TICKET:: {0}".format(self.tickets[-1]))
+            self.Log("TICKET:: {0}".format(ticket))