Style the deleted annotation message

Fixes #1607. @gergely-ujvari could you verify with this dokku: https://fix-deletion-placeholder.dokku.hypothes.is/

![screen shot 2014-11-04 at 16 10 55](https://cloud.githubusercontent.com/assets/47144/4901870/cd08ca36-6434-11e4-9da6-5eb4d073a7a1.png)