handle pcotomo

pcotomo must be handled.

It can contains several projections to be splited and create one NXtomo each.

We also must duplicate dark / flat in order for each NXtomo to be processed.

We must use tomo_n in order to know how to split the projection sequence. And nb_loop * nb_tomo to check all requested data are there.

The tricky part is that now we are collecting information from one sequence in order to generate one NXtomo. But for pcotomo we need to collect information from one sequence in order to generate several NXtomo. And dark and flats needs to be duplicated.