Support asynchronous non-market orders (#8946)

* Add 'asynchronous' parameter to trading api

* Add regression algorithms

* More fixes for asynchronous orders

* Fix failing unit tests

* Fix failing unit tests

* Add multiple orders requests in transaction handler

Make each transaction thread handle requests corresponding to the same order

* Refactor order state machine in BrokerageTransactionHandler

Now using a single dictionary to hold orders and their state, either pending for submission, open or closed.

* Revert: remove complete orders from new state machine in BTH

* Add order ticket to new BTH open orders state machine

* Run syn in Backtesting transaction handler for new orders submission

* Remove OpenOrderState.SubmissionPending property

* Add Security to OpenOrderState

* Minor fix

* Cleanup

* Some cleanup in BTH

* Cleanup

* Minor fix

* Minor unit test fix

* Minor fix

* Make Brokerage.ConcurrencyEnable property virtual

* Minor change

* Cleanup

* Add 'asynchronous' parameter to SetHoldings api

* Improve regression algorithms

Algorithm.Python/TrailingStopOrderAsyncRegressionAlgorithm.py

@@ -0,0 +1,26 @@
+# QUANTCONNECT.COM - Democratizing Finance, Empowering Individuals.
+# Lean Algorithmic Trading Engine v2.0. Copyright 2014 QuantConnect Corporation.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from AlgorithmImports import *
+from TrailingStopOrderRegressionAlgorithm import TrailingStopOrderRegressionAlgorithm
+
+### <summary>
+### Basic algorithm demonstrating how to place trailing stop orders asynchronously.
+### </summary>
+### <meta name="tag" content="trading and orders" />
+### <meta name="tag" content="placing orders" />
+### <meta name="tag" content="trailing stop order"/>
+class TrailingStopOrderAsyncRegressionAlgorithm(TrailingStopOrderRegressionAlgorithm):
+    '''Basic algorithm demonstrating how to place trailing stop orders.'''
+
+    asynchronous_orders = True