Show cohorts on the new instructor dashboard

TNL-161
Good question. I thought about this when I added it. This is a standard pattern throughout our code, so I didn't want to mess with it. Also, this does seem like a reasonable usage of ```id``` because there must only be one such template.

In general, using 'id' is discouraged because it has to be unique. It is all too easy to add a component to the page without thinking about the future when another instance might be added.  Even things that seem like they might be singletons (e.g. a header), can sometimes end up becoming something that gets used multiple times (e.g. there's an inline section that itself has a header).