More SIMPLE button styles for buttons and button bars

Summary: Ref T1460, this adds additional buttons colors and styles for use in inline comments. Will also backport to Calendar and PHUIInfoView

Test Plan:
Review new buttons and hover states in UI Examples.

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Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T1460

Differential Revision: https://secure.phabricator.com/D12162