Show cohorts on the new instructor dashboard

TNL-161
Nit: The body of this if statement is not indented (and neither is the one immediately below), but the body of the `for` loops on lines 101 and 111 are indented. I can understand the reasons behind each style, but it would be nice to choose one and be consistent. Seems to me like the tradeoff is between readability of the template vs the rendered HTML.