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. 
`filter_users` would be sufficient, also the convention in JavaScript is to use `camelCase` rather than `snake_case`, try to follow the conventions of the language you are coding in :grinning: