change segment's oversleep metric and related stuff to real segment duration setting

[volard]

I completely forgot about the possible case when the real sleep segment duration can be also

• shifted
• shifted and longer
• shifted and shorter and so on

So instead of saving only one oversleep metric, its better to save "real segment duration" (i.e. real start and end time)

[volard]

So of course oversleep, streak, lack of sleep, risk of adaptation failure is calculated based on provided real segments duration and position