Layout Phriction actions without floats, to avoid conflicts with floating content

Summary:
Ref T13195. If a Phriction page begins with a code block, the clear: both; currently makes it clear the action list.

Instead, use table-cell layout on desktops.

Test Plan: Viewed a Phriction page with an initial code block on desktop/tablet/mobile/printable layouts. Now got more sensible layouts in all cases.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: GoogleLegacy

Maniphest Tasks: T13195

Differential Revision: https://secure.phabricator.com/D19649