This patch contains massive refactoring of the abstract operations an…

…d internal slots used in the Sensor interface specification.

The refactoring goals are:

- Stop firing events synchronously.
- Reset internal slots values after stop.
- Fix logical errors in the abstract operations.
- Recompose abstract operations so that duplication of the algorithms steps is removed.
- Drop the unused abstract operations and internal slots.

Fixes #203
Fixes #218
Fixes #215
Fixes #204
Fixes #126
Fixes #243