discussion style changes

Changes
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- inline timestamps
- add permalink icon
- hide actions when discussion is closed
- change relative date format

![image](https://cloud.githubusercontent.com/assets/960919/4560825/ff9af7e6-4ef7-11e4-8ac4-abb8c9987e92.png)

This discussion about icons has been coming up a lot, therefore I've added it to our NGW engineering meeting minutes to be discussed next week.