Allow to change logdir/logfile path

- Provide single configuraiton option `logDir/logPath` in `config.yml`.
- Move `log4j.json` into `logger.js` like https://gist.github.com/tomaszdurka/c89886d2f7b9e926e5cf
Maybe call it `configure`. Actually it would be possible to only use `getLog` - it would allow usage of un-configured logger, right?