Memory usage and better notifications

In this release you'll notice that memory usage over time is fewer than before. It's because the server stores trades only for active tasks that uses trades data. Also the server will store trades that are used by client application, like for manual trading or just viewing a chart.
Also the server will attach instrument's symbol into notification object. It allows to click on notification and get trading page opened for that specific instrument. Like in situations when order is filled you can click on notification to open the trading page with it.