Fneves/failing deploys summary

This pull request adds an alert icon next to each deployment reference on summary page to each deployment where the last deployment was not successful.
When hovered, a popover will show when, by who and what release failed to deploy.

Screenshot:

![failed_deployment](https://cloud.githubusercontent.com/assets/647255/5243957/08c96a5e-7942-11e4-80e7-73b132106937.png)


/cc @zendesk/samson @pswadi-zendesk 

### References
 - Jira link: [SAMSON-124](https://zendesk.atlassian.net/browse/SAMSON-124) 

### Risks
 - None