## Issue
Closes 5721: Publish-Preview updates
## Changes
(1) Match the recent "incognito" change that sets the channel to `undefined` via `updatePublishForm`. This change would also cover `null` -- I don't think it's being used to represent something else, so showing "Anonymous" for `null` should be fine.
(2) Added channel icons, so it'll be more obvious to the user if they accidentally selected the wrong channel.
This option allows users to bypass the "publish preview" modal. Users can disable it by checking "don't show this again" in the modal, and re-enable it in the Settings Page.
