Add an HTML editor to chapter description text area

[jcn]

For now, this is the one text area that could use rich formatting. This would mean that trustees/deans editing the chapter description wouldn't need to know HTML.

I don't have a particular editor in mind, but it should be very simple, and be able to limit the formatting. I think we should limit this to: a, b, i, em, strong.

Fallback to regular form input should happen gracefully.

This could be implemented with HTML or with a Markdown editor - doesn't much matter to me.