reset assignment button for test users

Adds a reset button (well, link) that resets all assignments and tasks for an individual user. Only appears for email test+ users.
On Fri, Sep 05, 2014 at 11:07:27AM -0700, Brian Sadler wrote:
> Can you rename this reset_test_users?

It only resets the currently logged in user so that name would be inaccurate.