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)



Given the comment you're removing, I'd be cautious about this change.

Is the user serialized with a serializer? Does the serializer only send the data we need for drop downs? Maybe we should have two serializers, one for the full user object which we return for the current user, and one with only what's needed to populate the drop downs for all other users.