Process Remarkup in text and HTML email bodies appropriately

Summary: Ref T2617, adding inline styles to handle html email objects

Test Plan: Add code block to a Maniphest comment. Email should show pretty yellow background for code block.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T2617

Differential Revision: https://secure.phabricator.com/D10860