[logback-user] separate task log files (slf4j + logback)

[Денис Матвеев]

The MDC does not help when I have several different long-running tasks 
in one thread and I just want to immediately separate their logs. It 
seems that this is not such a fantastic wish. It is much easier to 
separate logical logging flows at once, than to filter them later in 
databases. The amount of data is large, logs per day can accumulate 
several hundred megabytes. It turns out that we will have to write our 
own implementation of such a log.