120 networker

networker skeleton
Rather than implementing a whole watcher, which will essentially be a StringsWatcher, why not just implement a base.Caller, which have a Call method that returns a nil error and empty []string results:
```go
// nopCaller implements base.Caller and never calls the API.
// Once we can watch networks, drop this.
type nopCaller struct{}

func (c *nopCaller) Call(_, _, _ string, _, _ interface{}) error {
    return nil
}
```

Then, in `worker/networker/networker.go`, change the SetUp() method like this:

```go
func (nw *Networker) SetUp() (watcher.StringsWatcher, error) {
    ... rest of the code
    return watcher.NewStringsWatcher(&fakeCaller{}, params.StringsWatchResults{}), nil
}
```

This will allow you to fulfill the worker interface, without having to implement a whole watcher which we won't use anyway.