Adding starttime and endtime parameters to Dynam-i

[marion-hoffman]

When creating windowed events, some right-censored events are added after the last dependent events. It would be better to remove them. This is true for all rate models.

I propose to just erase the extra rows ahen the windowed events are created, before preprocessing. I'll do this on the DyNAM-i branch for now and it can be added to the main if it works fine (@auzaheta you can check then if that's ok with you).

[marion-hoffman]

--> Correction: this can be done through the starttime and endtime parameters, which is not available yet for dynam-i, which I will correct (title changed).