Use recommended approach for logging.

This splits the logging logic into
```logging```, which becomes a client library, wrapping freedom.core().getLogger()
and
```logger```, a freedom module implementing the well known 'console' API, which
can be installed as a custom freedom logger, via
```javascript
freedom('manifest.json', {
  logger: 'logger.json'
}).then(...)
```

In doing so, we can remove the ```core.console``` permission from all other
workers, and the logs will include freedom system errors.


Addresses https://github.com/uProxy/uproxy/issues/503
we can certainly expose that in uproxy-networking. As you can see, the whole point of this division is that all of the log filtering happens centrally in the logger.  Moving it to each module self-filtering makes runtime changes to logging policy somewhat more complex, hence my preference for this design.

We'll expose ```setConsoleFilter``` through a secondary API in logger.json, as in the demo.