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This adds the ability to reply to notifications. :boom: :email:

It's super simple right now. Eventually it would be awesome to get all the autocomplete and file upload goodness that GitHub.com has, but…someday.

![github_notifications_and_testing_123__issue__1__bkeepers_test](https://f.cloud.github.com/assets/173/1806932/59de04b4-6cc7-11e3-8cb0-e594c9245de5.png)