Fix two issues with Remarkup in Pholio

Summary:
Fixes T10865.

• Mock descriptions did not markup.
• Image descriptions did not get a proper container <div />.

Test Plan:

• Created a mock with remarkup in the mock description and in an image description.
• Viewed mock detail.
• Saw list styles render properly in both mock description and image description.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10865

Differential Revision: https://secure.phabricator.com/D15793