Add a Read More link to PHUIDocumentSummaryView

Summary: Currently it's difficult to notice posts may be much longer than the summary (in most cases, actually), Adds a consistent "Read More" link to the full post. Also made sure "violet" was more consistantly used.

Test Plan:
Review summaries in Phame

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14827