Clocks should not allow unsetting segments when not in edit mode #1050
Description
Progress tracks explicitly only allow marking progress, not removing it. The only way to unmark progress is by editing the progress item and using the function there. This does not hold up for clocks, which allow unmarking progress by simply clicking an already filled segment. This should likely be blocked, since this could be a potentially destructive action - and clocks are generally only meant to advance, never to retreat. This problem is further amplified by the fact that reducing a clock does not state its original value, thus potentially losing information when clicked by accident.