Subscribing and unsubscribing

Not ready yet. 

- [x] write some specs for the controller around subscribing and then unsubscribing
- [x] clean up the duplication in the edit cluster service spec
- [x] @OllieJennings need your advise RE some CSS
- [x]  Fix a bug where if you unsubscribe, the star icon completely disappears (just need to update userCanSubscribe on $scope so the right element shows.