R1:02b59e685fb7

PHUIButtonView class

Summary: Rough pass at a PHUIButtonView Class. Keeps phutil_tag intact and adds some image features if you use the class.

Test Plan: UIExamples

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D6192