Implement Voting Behavior

We want to allow users to vote on submissions, so let's just do that.

Generally, we want to implement these actions with POST requests
(because GET requests are considered idempodent), but we'll ignore
this for now for the sake of brevity.
Add User Account System

Reddit really does not make sense if you dont have users, so let's
create a User Accounts System. Luckily, a lot of people need user
account system, which is why people have collaborated to create Devise,
so that you don't have to write your own.

We simply add it to our Gemfile, run `bundle` and
`rails generate devise:install`. We can then create our User model by
`rails generate devise User username:string` and some minor modifications
to app/models/user.rb et voila, we have users in our system.

We then run `rails generate devise:views` to be able to modify devise's views
to add the username to the form.

(Don't forget to run `rake db:migrate`)