Make comments polymorphic

* Users can comment on plays, media, and even other comments
* Users can see their comments instantly pop up near what they commented on
so `serialize()` gives this weird string like `"commentable_type=Comment&commentable_id=44&body=something"` and `serializeArray()` gives me this array of JSON objects but I would have to pass in `comment[0]["value"]` `comment[1]["value"]` `comment[2]["value"]` to the comment_params, is this the best way?