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).
I wasn't aware of that. I figured all you really needed was the grader membership IDs to unassign TAs. It isn't hard so I'll try to get that working, I need to refactor the grader_manager anyway.