Add users count to Members index page

PT Link: https://www.pivotaltracker.com/story/show/76852906
Screenshot for the feature: 
![5591015](https://cloud.githubusercontent.com/assets/3853353/3949332/021b94fa-26b5-11e4-8c50-aa2127764d95.png)

- Added cucumber test for this story
- Added couple of new cases to the page's view
- Added @users.count to the view so visistors could easily see the number of users participating in AV.