Typeahead roles

Adds roles to the typeahead dropdown.

Looks like this:

![screen shot 2014-10-01 at 9 59 20 am](https://cloud.githubusercontent.com/assets/1903518/4476139/2bb04f8c-4973-11e4-944b-da5a988d916c.png)

- shows collaborators on top, but shows duplicates. We are planning on fixing that issue with the migration to select2

Example:

![screen shot 2014-10-01 at 10 00 20 am](https://cloud.githubusercontent.com/assets/1903518/4476153/4e1a06ee-4973-11e4-8005-19f02ee8e799.png)



Aaand I was thinking of a different spot in the code.  Aaron is saying that the typeahead thing expects a different payload format than the standard ember data one.  
If they were serializing everything by default [the docs](https://github.com/rails-api/active_model_serializers/tree/0-8-stable#arrays) say they'd get something like `{users: []}` and their component must expect just `[]`.  Maybe it'd be better to change the component like he mentioned.