SKILL-3: As a guest I can receive course details by id

Good point that it's something missing...
I think it should be json about the type (and ruby 2.x style for hash).

Would you please do me a favour ...
```ruby
class Api::V1::ApiController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound do
    head 404, content_type: 'application/json'
  end
end
```
We need such controller and then change inheritance.

Of course I am open for discussion if you don't like the idea...