[WIP] Improve logging layer

[golyshevd]

1. Reduce log levels of some annoying messages, also increate theirs detaization
2. Kill feature: give units own loggers, now units, can have own logging settings.

var app = fist({
    logLevel: 'LOG'
});

app.unit({
    name: 'foo',
    settings: {
        // easy to develop
        logging: {logLevel: 'DEBUG'}
    }
});

3. Log server._connectionKey on listening

TODO: Update docs