Logger for pyDKB

[mgolosova]

We need to add some kind of the common logger for the Dataflow stages and the library itself to avoid manual formatting, writing to sys.stderr, etc.
The logger should:

• be aware of different log levels (fatal, error, warning, info, trace);
• accept one message or list of messages;
• coordinate formatting of message lines with Kafka ExternalProcessLogger [1];
• never forget about newline in the end of message (as we often do, writing then manually);
• output messages to the STDERR;
• add timing to the messages [2];
• add info about the program produced the message [3].

There are, of course, some loggers for Python that can be used (say, logging). They should be studied to see if there`s a standard solution for we need (I think there must be, as we`re not looking for something extraordinary), and if found -- introduced to the common workflow. If -- al of a sudden -- nothing appropriate was found, implement the custom logger.

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[1] The suggestion is to leave already existing agreement about starting the message with smth like (ERROR) (or any other log level marker), but also teach Java part to take (==) as "same level as above" for multiline messages. Having a lot of (ERROR)s in the log looks ugly.

[2] Then we must teach Java part to remove this timing, as it will be added via Java logger as well.

[3] Then Java part must not add the information about the external command, form which STDERR the message was taken.