Unsubscribe from /subscriptions

This adds an unsubscribe button ("remove") to the subscriptions list.

closes #975 

![screen shot 2014-12-01 at 12 12 12 pm](https://cloud.githubusercontent.com/assets/1239550/5240242/55db1eda-7953-11e4-89f2-e3f8d8f90e20.png)

Shouldn't it say "Unsubscribe" so we've got consistent language?