React tables

This is a redo of #1502. I have done some architectural restructuring so that the base Table React component is more generalizable, and I've changed the way components get mounted onto the view (originally was using the react-rails gem, but now going a more native route). Also deleted unnecessary .rjs files (for the original tables) and partials, as well as the students' populate route in route.rb (we now populate by sending an AJAX request to the same url, just requesting it in JSON).
If we decided to not have `and` at all, then this can just be `return render ...`. The `render` call can also be in one line. Personally, I also don't think it's bad to have a separate return statement on its own.