Previously, we assumed that plain text should always be Markdown-escaped

for editing purposes. However, when Markdown becomes optional, we won't

always want to do this. Instead, we want to take the user's settings

into account, and only escape if the text isn't already in Markdown and

the user has chosen to edit in Markdown by default.
A couple of new Markdown utility functions were added to normalize text

for editing and for determining if a user wants to edit in Markdown by

default. The latter is hard-coded to True right now.
New template tags have been added for this new normalization. The old

markdown_escape filter has been removed. Templates now contain the

proper edit state for the user.

Unit tests pass.
Toggled the user default on and saw that all Markdown fields on review requests

and review replies were showing up as Markdown, and that plain text fields were

being escaped for edit.
Toggled it off and saw that both Markdown and plain text fields were represented

as-is, without any escaping.