addition of active admin admin_user feature with failing javascript test

the feature includes a failing javascript test which can be rectified
as soon as a decision is made on which headless drivers we are using
for capybara
finished admin admin_user features including testing delete

part of pivotal tracker story https://www.pivotaltracker.com/story/show/76232594

CHANGES
1. addition of gems for headles javascript testing (currently delete popups)
  - capybara-webkit
  - poltergeist
2. Implementation of admin admin_user feature
3. modify cucumber enviroment to use poltergeist (phantomjs) by default
Tidy Gemfile and remove duplicate field from admin user list view

part of pivotal tracker story https://www.pivotaltracker.com/story/show/76232594

CHANGES
1. Change double quotes in Gemfile to single quotes
2. Change gemfile hash to modern style version
3. remove duplicate email field from list view of activeadmin AdminUser
moved "given I am an authenticated user" to background task
added addtional scenario testing create functionality

part of pivotal tracker story https://www.pivotaltracker.com/story/show/76232594
added create story that was missing identified by by cucumber only showing 1 fail
on a bug that affected 2 view
clarified comment and redfactored method creating admin_users

part of pivotal tracker story https://www.pivotaltracker.com/story/show/76232594
1. clarified comment about why we do not need to confirm javascript dialog box
2. refactored method that makes admin users from a table to be more concise
Merge pull request #22 from PurityControl/admin_user_feature

Admin user feature