Preserve line breaks in standard remarkup fields

Summary: Initially the change is aimed to solve issue with line breaks being lost in projects descriptions. But it is done in a general place so line breaks behavior is more consistent all over the place.

Test Plan:
- Write a multiline description of the project, using single \n for line breakers.
- View project details in project/view/X?

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10014