Test cohort selector in NewPostView

@jimabramson @andy-armstrong @cahrens @dan-f 
I'm not sure if you're asking why it was added at all or why it was added in this particular location. The answer to the first is that the dummy template that was previously used did not conditionally render the cohort selector based on moderator status, but the real one does. The answer to the second is that this block is testing that selecting particular topics enables/disables the drop-down correctly, which requires moderator status.