Let's add Comments

Let's give people an outlet to troll. We simply create our model
`rails g model Comment text:text user:belongs_to submission:belongs_to`
and `rake db:migrate`, add some validations and change the appropriate
views. Baam.
Add Comments via Web

We can simply create a controller Comments with
`rails generate controller Comments` and create the necessary actions.
That's it.
Implement Ordering

We can implement simple ordering through either default_scope or
ordering directly in the controller.