Add users count to Members index page

PT Link: https://www.pivotaltracker.com/story/show/76852906

- 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. 
I am new to the project, so I am not aware of detail, but I'd like to know as well... I basically repeated the same test twice, because I added a cucumber test for this as well.