image links in hdf5 and second round on scan_meta

closes #689 (closed) and more:

• second round on scan_meta:
  • split fill_meta into two functions, one evaluated on scan::init ; the other at the end of an scan
  • remove traces of scan_info in the scan_meta related calls
  • implement fill_meta in lima
• fix issue in _get_filenames of LimaDataView and adding related tests
• adding image reference to hdf5
• writing 'instruments' and 'scan_meta' at the end of the scan to hdf5

Fix #775 (closed)