Design changes for moderated posts

Sat down with May. Did the design thing.

Changes:
* Add Flow global less variables to ensure consistency
* Correct indent so text is lined up with topic heading
** Ensure highlighting special cased
* Visually separate topic summary with dotted line
* Closed topics now have no background color
* Author hidden for closed comments when collapsed

As design spec in:
https://trello.com/c/Ypug2Kdl/337-c-10-closed-topic-colors-remove-the-faded-gray

Change-Id: I0519643a1c0c398bcec124664359bc97e65effdc
Merge "Design changes for moderated posts"