Adds IFU support

Adds features required for IFU integration or developed during the integration:

  • Adds support for IFU files in gris_translate_headers
  • Adds IFUFitsFile subcalss to GrisFitsfile
  • Adds WCS generator for IFU data
  • Added gris_parse_calib script to retrieve reduction settings from IDL scripts
  • Switched WCS generation to structure using ABCs with more structured interface
  • Removed too specific test for coordinates