Add CSS to wrap long tables in a scrollable area

Summary: Fixes T9609, applies style to a wrapping div for long tables in Remarkup

Test Plan: Build a long table in Phriction, get scrollbar.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T9609

Differential Revision: https://secure.phabricator.com/D14355