[h5_to_nx] handle zserie

Description / Goal

handle zseries by creating one entry per z found. /close #13 (closed)

We can still create one file per entry (default behavior of tomoh52x) or create one file per entry and one master file (--single-file option)

TODO

• 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.
• add _ZSerieAcquisition class: represents a serie of _StandardAcquisition. 'write_as_nxtomo' is now only part of StandardAcquisition
• doc
• test

NOTE

Split H5_INIT_TITLES to H5_INIT_TITLES and H5_ZSERIE_INIT_TITLES to distinguish zseries and 'standard acquisition'

No API modification at command line level. Only adding an init_zserie_titles option to define zseries title if necessary