Update PholioMockView Styles.
Summary: Less janky sidebar, new 'photoshop-like' texture for image background.
Test Plan: Tested mocks with and without side comments, hover over marked squares. Tested small and large images.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D5216