Stock exchange updated
Merge branch 'master' of https://github.com/legartis/mentoring-sushytskyi

Conflicts:
	practice/tasks/Observer/StockExchange/StockExchange/IBroker.cs
	practice/tasks/Observer/StockExchange/StockExchange/IStockExchange.cs
	practice/tasks/Observer/StockExchange/StockExchange/IStockExchangeListener.cs
	practice/tasks/Observer/StockExchange/StockExchange/Program.cs