locale property Null safety

1. irte_engine
2. app_settings.model
3. AppSettings
4. locale property

AppSettings class

1. Constructors
2. AppSettings
3. Properties
4. hashCode
5. isMetric
6. locale
7. props
8. runtimeType
9. stringify
10. Methods
11. copyWith
12. noSuchMethod
13. toString
14. Operators
15. operator ==