Add support for markdown in the blog app for linking external media

[baconz]

[esoergel]

Right now They display with

 formatting, but no outline, special background, and a normal (not monospaced) font.  It's a temporary fix.

[thadk]

Lets enable blog posts with the ability to markdown link outside resources (Flickr, YouTube) and upload a single picture to S3 for each blog post.