Make message to course coordinators markdown
In the message to course coordinators we support markdown, but the actual field is not a WYSIWYG editor.
- Change the user-facing course proposal page to have an editor for this field
- Always render this as markdown in the management panel. Remove button to switch between plain text and markdown.
- Always render this as markdown in the user interface. Remove button to switch between plain text and markdown.
- Change management edit interface to show an editor when editing this field.