Task - time tracking enhancements



- Protect from instant completion: the task can be completed only after half of the task.minutes elapsed - turn on / off per task
    - Maximum tracked time is e.g. 50% more than task.minutes (global.tracked_time_limit = 0.5)
- task.minutes is updated: task.minutes = task.minutes x (1 - weight) + tracked x weight
    - global.updatetime_weight = 0-100% (default 50%)
