models/step_session library

1. step_logger package
2. documentation
3. models/step_session.dart

step_logger package

1. Libraries
2. models/step_logger_config
3. models/step_session
4. services/background_service
5. services/step_service_android
6. services/step_service_ios
7. step_logger
8. utils/notification_utils
9. utils/notification_utils_ios