Warning timeout2

This is a inactivity warning timeout solution for javascript enabled browsers. It uses https://github.com/krishnasrihari/auto-session-timeout-warning.  Javascript disabled browsers still use the no_keep_alive version.

To see it in action, edit these lines in development.rb
  Devise.setup { |config| config.timeout_in        = 1800 }
  config.session_timeout_warning_seconds    = 90
  config.session_check_frequency                     = 60