CB-6000 handle task info events from WS

[SychevAndrey]

1. AsyncTaskService was moved to core-root to avoid circular dependencies
2. Task is added to tasks map only when getter brings data from backend to save real task ID (AsyncTask.create)
3. updateStatus method was added to update task status on websocket message if task is running
4. When running prop is changing to false, we request gql endpoint
5. Naming improvements (onEvent return type Subscription -> Unsubscribe) to avoid confusion with Rx Subscription plus it's basically returns cancel function, not subscription in any sense.