This adds checkboxes below the text fields in the Review dialog for

toggling Markdown support. It also loads the correct values from the

API, depending on the user's defaultUseRichText setting in UserSession.
If the default is to use Markdown, the review and comments will be

requested with text normalized to Markdown, and all TextEditorViews will

be set to save as Markdown by default.
If the default is to use plain text, the review and comments will be

requested without any text normalization, allowing the default values to

come in. All TextEditorViews will therefore reflect the stored value.
Toggling the new "Enable Markdown" checkbox for any field will mark that

field as dirty, so that it will be saved when saving or publishing the

review. That will then be saved along with the appropriate Rich Text

setting.

Tested loading the body and comment fields with both Markdown and plain text

flags set, and with different defaultUseRichText values set.
Tested saving with both Markdown and plain text.
Viewed the payloads to make sure we were loading what was expected.
Unit tests pass.