roll out was balking on conflict with db/schema.rb, so always revert changes on prod before roll out.
Add admin-nav to top.
Put lesson_plan.content in <pre> for scaffolding.
Give good error message if exercise is missing a description.
Don't indent the inside of a <pre> tag
Put admin header on top of all pages.
Parse content for handout and topic
Don't narrow width on admin pages.
Change ` to <code> and put <a> around links starting with http/https:
Removed obsolete comment.
Don't expect every exercise to have a unique dir; instead refer to them by lesson & order-in-lesson.
Using + for a bullet makes a expanding/collapsing bullet.