- 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
- `GetCashBalance()` will return a `List<CashAmount>`, will not need to
set conversion rates, which requires knowing what the account currency is.
- Removing `Global.Holding` conversion rate field. It wasn't being used
and required knowing what the account currency is.
- Adding equality operators for `CashAmount`. Adding unit tests.