Enable account story embedding

[scottwittrock]

Enable the ability to embed an account story like you can with TinySheets.

We could do an insight article like this.

[johnholdun]

Some thoughts for whoever picks this up:

1. The simplest way to do this is to just give the user an iframe that points to the current URL.
2. To make the experience a little nicer, we probably want to create an embed mode that hides the menu and maybe changes the padding. This is probably best done with an extra query parameter (i.e. embed=true) that we add into the URL that's part of the iframe code
3. The final step is adding a "Share" or "Embed" link that lives beside the "View source" link and reveals the embed code right below it. The treatment for this can be identical to how the "View source" link reveals the source code.