Show bytes sent/received in simple socks

Sample output in background page:
![image](https://cloud.githubusercontent.com/assets/8723127/4425242/8d0f96d6-45a7-11e4-9db6-ce459ece7534.png)

Let's use the logger here, e.g.:
```typescript
log.debug('Getter received ' + ... );
```

I'm suggesting debug so that the console isn't flooded by messages in the normal case. It's just good to have the option to enable these.