Refactored AkismetHelper into AkismetService and cleaned up `Spammable`

app/controllers/admin/spam_logs_controller.rb

app/controllers/concerns/spammable_actions.rb

app/models/concerns/spammable.rb

app/models/issue.rb

app/services/akismet_service.rb

app/services/issues/create_service.rb

app/services/spam_check_service.rb

app/services/spam_service.rb

app/services/system_note_service.rb

db/migrate/20160727163552_create_user_agent_details.rb

...igrate/20160729173930_remove_project_id_from_spam_logs.rb

lib/api/issues.rb

lib/gitlab/akismet_helper.rb

spec/controllers/admin/spam_logs_controller_spec.rb

spec/controllers/projects/issues_controller_spec.rb

spec/lib/gitlab/akismet_helper_spec.rb

spec/models/concerns/spammable_spec.rb

spec/requests/api/issues_spec.rb