- fixed bug that caused too much sensing after changing relative level or screen off/on
- note: this bug is only partially solved, in theory it would be good to be able to cancel pending starts and start right away when desired (e.g. if checking every 60 secs, when a person turns on screen and next scheduled check is in 30 secs, it should cancel that one and check right away)
- fragment really checks if activity is running (like before, not just checking setting) when resuming
- added sense interval to preferences
- moved several constants to Data class
- created strategy style pattern to swap screen brightness algorithms