Add fluid-view as an option for PHUIDocumentView

Summary: Fixes some UIExample UI issues, adds a new full-width setting for DocumentView

Test Plan:
Test UIExamples at desktop and mobile breakpoints

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7431

Differential Revision: https://secure.phabricator.com/D11933