tweaking activity feed

- add "Class activity" label, and Newsfeed filters above the
  newsfeed http://cl.ly/image/0v0t1D3V2f1K
- move the feedback item action icons inside the item containers
  http://cl.ly/image/161S1K3E283w
- When upvoting, the counter pushes the downvote button to the right,
  seems a bit off to me http://cl.ly/image/2M003c2o2i1f