Add users filtering to the members index page

PT Story URL: https://www.pivotaltracker.com/story/show/76849484
Heroku instance: http://damp-lowlands-2351.herokuapp.com/users

Adds users filtering to the members page using JS. 
to have label is advised by HTML5 standard, but it can be hidden, so it is available only for screen readers (for blind people that is)