Let user connect components with lines

Yes we can do it the same way I trigger the `go:campaignDesignerRepaint` event. We use the `$rootScope` as the event dispatcher. It can be injected into any service. So:

```
$rootScope.$emit('go:campaignDesignerError', {message: "Could not connect components"});
```

then in the directive:

```
$rootScope.$on('go:campaignDesignerError', function (event, error) {
    alert(error.message);
})
```