easier templates for "Note:", "Danger:" info boxes

Created by: seancolsen

@ErichBSchulz made some edits recently where he created breakout boxes with icons for "information" and "danger" messages. Here's an example (there are a few in this page).

I thought this was cool and it got me thinking about how we could make this sort of content more intuitive to create and more visually appealing when rendered.

I found an extension called Admonition that does exactly that. I'd like to play with it a bit to evaluate if it might be worth using in the Dev Guide and/or other guides.