Flash light option during scan

- Implement safe way to turn on/off flash. Because auto focus and flash are concurrent.
- Callback to change flash status.
- Change UI.

https://jira.nkey.com.br/browse/NICANDROID-104
Flash light option during scan

- Flag to prevent user from clicking flash while it is turning on/off.
- Add progress bar while flash is turning.

https://jira.nkey.com.br/browse/NICANDROID-104