Added Kaminari for pagination of cats and reviews.

9 Cats per page on index, 3 reviews per cat shown.
You can simplify this a bit with a ternary operator:

```HTML+ERB
<li><p><strong>Description: </strong> <%= @cat.description.empty? ? "(none)" : @cat.description %></p></li>
```

The ternary operator is a condensed `if/else` statement and should be used sparingly but in this case it would be OK:

```ruby
if some_condition
  true_branch
else
  false_branch
end
```

is simplified to

```ruby
some_condition ? true_branch : false_branch
```