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. 
cucumber is an integration test, i.e. it test view, controller, model, routing, etc.
view specs is a unit test to test how the view renders whatever data is supplied to it.

In WSO, in cucumber tests we test more for content, e.g. I should see 'My big text', and in view specs - we test more for structure of the UI, e.g. has_selector, has_class, within form...etc.