Clean up the mess related to configure_from_file and configure_from_dict

[tintoy]

Note: this PR is a rebase of PR #78 by @piotrmaslanka as part of the work in #92.

Since this introduces some breaking changes, I'd invite @tintoy to express what should be left.

Right now everything can be configured using logging.config.dictConfig() including CLEF, override_root_logger and use_structured_logging

Also, this adds an option for ConsoleStructuredLogHandler to output to stderr. It's a config option.

I've tested it on my staging environment.

Also, I wonder, because right now by configuring one handler you can change the feature flags globally (for other loggers), shouldn't we move that to private properties of SeqLogHandlers? Because this behavior is not immediately obvious and somewhat astonishing.

Also, current implementation allows you to configure whether to use CLEF on the level of a ConsoleStructuredLogHandler, which is a code smell (and just plainly doesn't make sense, as a ConsoleStructuredLogHandler will never have to deal with CLEF), which amounts to, how one physicist put it as "spooky action at a distance".

I suggest we slowly shift towards per-handler configuration instead of global feature flags.