refactoring: removed unnecessary .each_with_index
Moved responsibility for getting multiple users to new class Academy

badges.rb: moved out method get_users_badges to academy.rb
Created academy.rb: moved in get_users badges and renamed to get_cadets
lib/codebadges.rb: added require statement for academy.rb
bin/codebadges: changed method call to new name get_cadets
spec/badges_test: changed method call to new name get_cadets