Support embeds

[johnholdun]

Adds UI to each story that exposes an embed code, as well as a new render mode that alters the UI a bit when the story is embedded.

Closes #46

[ginatrapani]

This is very cool!

• 1 question: How can we make it so the whole embedded story appears, and it doesn't scroll inside the embedded area?
• 1 feature request: Can the embed code have the option to not show the title of the story at the top? We don't have to add UI for this, it can just be a title=true/false param on the embed src.
• 1 other question: Thinking about the Insights piece to show this off, I want to make sure: it's possible to embed multiple accounts on 1 page, right?