[FEATURE ember-routing-add-model-option] Enable by default.

As discussed in the core team meeting on 2014/02/28.

http://emberjs.com/blog/2014/03/04/core-team-meeting-minutes-2014-02-28.html
Merge pull request #4477 from rjackson/enable-ember-routing-add-model-option

[FEATURE ember-routing-add-model-option] Enable by default.