[Finishes #79484946] Free play links on student dashboard and puzzle headers

Links to the k1 version of Playlab and Artist free play when the user is in a k1 course.

![screen shot 2014-09-29 at 3 25 53 pm](https://cloud.githubusercontent.com/assets/413693/4450618/a12a4684-4827-11e4-83c8-b6cdf1cdc87c.png)

![screen shot 2014-09-29 at 2 37 00 pm](https://cloud.githubusercontent.com/assets/413693/4450623/afceaf36-4827-11e4-961d-3f893315baa3.png)

Moved to ApplicationHelper in 42c1b08, see if you think the `get_freeplay_url(type)` method makes sense.