- 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
Adds concept of Subscription to contain everything a data feed needs in order to process single data feed item
Moves preparation of all data to data feed thread, algo thread receives data in format it needs
QCAlgorithm.SetUniverse( func ) allows selection based on market/symbol/dollar volume/price
Remove laziness from Slice as optimization, no order by in real time handler