main library Null safety

1. unicon
2. main library

unicon package

1. Libraries
2. abstract
3. api
4. app_bar
5. article
6. articles_list
7. background_service
8. calendar
9. categories_list
10. category
11. centered_circular_progress_indicator
12. config
13. database
14. event
15. events_list
16. filters
17. geofr
18. headless_background_service
19. homepage
20. list
21. main
22. news
23. notifications
24. places
25. text_page
26. utils