handler/default_user_properties_handler library

1. databuckets_event_tracker package
2. documentation
3. handler/default_user_properties_handler.dart

databuckets_event_tracker package

1. Libraries
2. databuckets_event_tracker
3. databuckets_event_tracker_config
4. handler/default_user_properties_handler
5. handler/event_storage_handler
6. main
7. model/event
8. scheduler/event_sending_scheduler
9. utils/app_info_util
10. utils/common_properties_util
11. utils/device_info_util
12. utils/event_date_util
13. utils/event_size_util
14. utils/firebase_installation_util
15. utils/geo_info_util
16. utils/install_day_util
17. utils/json_util
18. utils/log_util
19. utils/prefs_util
20. validators/event_key_validator