Transfer Ownership

closes #3087
- added modal
- added controller
If updated_by and created_by are available on the role model I get the following error:

```
"Assertion Failed: You defined the 'roles' relationship on ghost@model:user:, but multiple possible inverse relationships of type ghost@model:user: were found on ghost@model:role:. Look at http://emberjs.com/guides/models/defining-models/#toc_explicit-inverses for how to explicitly specify inverses"
```

It seems to me that Ember is a bit overambitious in creating a relationship between user and role. Although it is often the case that there is a relationship between `hasMany()` on one model and `belongsTo()` on another model we don't have a direct relationship here.