widget/update_card library

1. desktop_updater package
2. documentation
3. widget/update_card.dart

desktop_updater package

1. Libraries
2. desktop_updater
3. desktop_updater_inherited_widget
4. desktop_updater_method_channel
5. desktop_updater_platform_interface
6. updater_controller
7. widget/update_card
8. widget/update_dialog
9. widget/update_direct_card
10. widget/update_problem_report_dialog
11. widget/update_sliver
12. widget/update_widget