Avoid code duplication for saving HDF5 files
core/data/DataSet.cpp has a function
saveHDF5 to store data in HDF5 format.
This repeats essentially the functionality of
ExperimentExporter, with some minor differences (eg., the name of the HDF5 Groups).
This function must be removed, since it might lead to inconsistencies in the exported data format; instead,
ExperimentExport methods must be used.