Polish and more embeds

This starts out as a few bugfix/polish fixes that I was working on then veers to embeds.

* 396f543: Example of a new-style URL `/live/t4eim4330dxh` vs. old-style: `/live/7jikpyx3yei6hlmbfintwaizsq`. Explanation of the algorithm: http://engineering.custommade.com/simpleflake-distributed-id-generation-for-the-lazy/
* 817f01a: Fixes an issue where you get a bunch of separators stacking up next to each other.
* 3d870c5: Simple visual fix for narrow screen mode.
* e2304fc: An update like "http://youtube.com/whatever\n\nSource: http://youtube.com/whatever" would accidentally replace both the links despite only the first one being an embed according to our embed semantics. This fix was requested by the UkrainianConflict people.
* 66c47e9: Adds a scraper that is only used when the Embedly-oembed and twitter scrapers fail.  This one makes an Embedly card for the URL which is useful for static photos (on e.g. imgur or instagram) or news articles etc.

![banana](https://cloud.githubusercontent.com/assets/338853/3379394/20e44c04-fbf1-11e3-8d11-009860639b2e.png)

:eyeglasses: @umbrae