Export sparse dataset (from Jungfrau detector) to Eiger-like files

[kif]

Multiple options are possible:

• Lima-like HDF5 files
• Eiger-like HDF5 files
• NXMx nexus format
  - preferred by beam-line staff
  - cannot be read back by FabIO !
  To be charged to ID29, serial crystallography project.
  @vasole any input on this ?