Add episodes"

Reverts LaunchAcademy/south_park_reviews#23


Instead of repeating this form in both the new and edit templates, you can extract it out into a partial:

```html
# app/views/episodes/_form.html.erb

<%= simple_form_for episode do |f| %>
  <%= f.input :title, required: true %>
  <%= f.input :release_date %>
  <%= f.input :url %>
  <%= f.input :season, collection: 0..24 %>
  <%= f.input :episode_number, collection: 0..24 %>
  <%= f.input :synopsis %>
  <%= f.submit %>
<% end %>
```

Which can then be used in your two views:

```html
# app/views/episodes/new.html.erb

<%= render "episodes/form", episode: @episode %>
```

http://guides.rubyonrails.org/layouts_and_rendering.html#using-partials