Requirements: Part 2 - Event Listeners

- As a user, I want to see 3 category(type) buttons printed at the top of the page. Each should be a different color. These can be hard-coded.
- I want to be able to click one of the 3 buttons, then only the cards that are in the category(type) should show.
- There should be some way for the user to unfilter the results (ie All Pets button).
