Sensor class

1. Properties
2. activated
3. hasReading
4. onError
5. timestamp
6. hashCode
7. on
8. runtimeType
9. Methods
10. start
11. stop
12. addEventListener
13. dispatchEvent
14. noSuchMethod
15. removeEventListener
16. toString
17. Operators
18. operator ==
19. Constants
20. errorEvent