Add Icon component to Showcase

[supermacro]

There is already an implementation of Icon, but I have not taken the time to create a page for it in the showcase.

Implementing this page depends on other components existing, such as input (If you are to make it look just how it looks on https://ant.design/components/icon/)

Desired outcome:

• Add a Icon page to the showcase
• Replicate as much functionality as shown in https://ant.design/components/icon/ with the current Elm Antd API