Component builder completion fix

This seems to give overall better codecompletion and reduce some of the errors mentioned here https://github.com/aduros/flambe/issues/216#issuecomment-33846014

With the fix in Entity this works like expected
```
var sprite = owner.get(Sprite); // no variable type defined.
sprite.[try auto-completion here, fails before, now works]
```
And the check in Component reduce ComponentBuilder errors.