chore: applied dart fix suggestions

[axl89]

It's not much; but it's honest work:

axel@cursed:~/projects/android/Best-Flutter-UI-Templates$ dart fix --dry-run
Computing fixes in Best-Flutter-UI-Templates (dry run)... 1.4s

65 proposed fixes in 11 files.

best_flutter_ui_templates/lib/app_theme.dart
  deprecated_member_use • 7 fixes

best_flutter_ui_templates/lib/design_course/design_course_app_theme.dart
  deprecated_member_use • 7 fixes

best_flutter_ui_templates/lib/fitness_app/bottom_navigation_view/bottom_bar_view.dart
  duplicate_import • 2 fixes

best_flutter_ui_templates/lib/fitness_app/fitness_app_theme.dart
  deprecated_member_use • 7 fixes

best_flutter_ui_templates/lib/fitness_app/my_diary/meals_list_view.dart
  duplicate_import • 1 fix

best_flutter_ui_templates/lib/fitness_app/ui_view/title_view.dart
  deprecated_colon_for_default_value • 2 fixes

best_flutter_ui_templates/lib/hotel_booking/calendar_popup_view.dart
  deprecated_member_use • 1 fix

best_flutter_ui_templates/lib/hotel_booking/filters_screen.dart
  deprecated_member_use • 2 fixes

best_flutter_ui_templates/lib/hotel_booking/hotel_app_theme.dart
  deprecated_member_use • 28 fixes

best_flutter_ui_templates/lib/hotel_booking/hotel_home_screen.dart
  deprecated_member_use • 7 fixes

best_flutter_ui_templates/lib/hotel_booking/hotel_list_view.dart
  deprecated_member_use • 1 fix

To fix an individual diagnostic, run one of:
  dart fix --apply --code=deprecated_colon_for_default_value 
  dart fix --apply --code=deprecated_member_use 
  dart fix --apply --code=duplicate_import 

To fix all diagnostics, run:
  dart fix --apply