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)



I understand that an array is preferable for things to work on the client side. I just don't remember seeing `root: false` sprinkled throughout our controllers (though I didn't look again) and this stood out to me, so I thought I'd ask.

Check this out:

    $ git grep render app/controllers/ | grep root
    app/controllers/affiliations_controller.rb:    render json: Institution.instance.names, root: :institutions
    $ git grep respond app/controllers/ | grep root
    app/controllers/admin/journal_users_controller.rb:    respond_with users, each_serializer: AdminJournalUserSerializer, root: 'admin_journal_users', journal: journal
    app/controllers/admin/journals_controller.rb:    respond_with journals, each_serializer: AdminJournalSerializer, root: 'admin_journals'
    app/controllers/admin/journals_controller.rb:    respond_with Journal.create(journal_params), serializer: AdminJournalSerializer, root: 'admin_journal'

There don't appear to be any `root: false` instances in our existing code base.