Support adding cohorts from the instructor dashboard

TNL-162
It depends whether the view owns its own element, or whether it is piggybacking on an element that is already in the template. If the view owns its own element then calling remove will remove it from the DOM and perform all the necessary clean up. If it doesn't own its own element then we can't call remove because it removes the passed in element from the DOM, so in that case we have to do the correct cleanup ourselves.

Having done this a few times, my preference now is to let the view create its own element and then insert it in the right place, rather than having to put empty parent divs in the template for every dynamic view that might need to be added. I feel that this is cleaner and removes the need for us to be careful about clean up.

If you think it will be less confusing I can change the other views to do the same thing.