Convert to component set

[knownasilya]

Maybe something like:

{{#ivy-sortable content=users as |user|}}
  {{#ivy-sortable-item}}
    {{user.name}}
  {{/ivy-sortable-item}}
{{/ivy-sortable}}

The reason I bring this up, is due to the {{collection}}s difference from all the other elements. I can see it going away, in favor of a component or a custom addon.

[knownasilya]

{{collection}} helper is being removed in Ember 2.0, see http://emberjs.com/blog/2015/05/24/another-two-oh-status-update.html