Move simple buttons, bar to own CSS file

Summary:

• Add a simple green button... maybe don't need
• Fix tokenizer search icon
• Splite simple and button-bar into own files

Test Plan: uiexamples, various pages with buttons, diffusion

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18063