UserSession now has a 'defaultUseRichText' flag (currently hard-coded to

true) that indicates if text fields should always default to Markdown

when saving.
If set, TextEditorView will force any text field to be in Markdown mode

initially when open, even if the richText attribute passed to it is

false. This is to keep with the current behavior where plain text fields

(such as those filled in by rbt post) are set to save as Markdown for

any modifications.
(Of course, that only works if the plain text coming in is escaped for

Markdown, which is the responsibility of the caller. A comment above

this new code explains that assumption.)
If the default for the user is not to use Markdown, then the text field

will reflect the provided richText setting.

Unit tests pass.
Tested manually with different combinations of incoming richText values

and different user defaults.