Icon Review Updates

[Darper]

Make the following changes found during a code review of the Icon component:

• Update classes in docs from "fa" to "fab"
• Update docs to tell user to include their own icon library and update classes
• Include code snippet to show how to use font-awesome
• Mark icon prop as required
• Remove console.warn on line 14
• Allow ...others
• Remove onClick as it is included in ...others
• Change large to compose from .font-size-1 and small to use .font-size-5