- add a new parameter in settings 'H5_ZSERIE_INIT_TITLES'
  will be merge with 'H5_INIT_TITLES' when h5_to_nx is call
- split _Acquisition into a base class (_BaseAcquisition and _ZSerieAcquisition). PR of ID15 data will need to be rework due to this I guess.
- _ZSerieAcquisition is a serie of _StandardAcquisition. 'write_as_nxtomo' is now only part of StandardAcquisition