Philippe 19/09/2019: CDF2CDF: add possibility to provide a fallback file if some information are not found in the input file

(cherry picked from commit bc1461b3)

Philippe 13/12/2018: split mode_netcdf module into multiple modules + add new subroutines to check if a file has been closed correctly
This is done:
*to reduce circular dependencies problems
*to have cleaner code
*to compile faster
*to detect problems with not correctly closed netCDF files

Philippe 05/12/2018: cdf2cdf: better support for older files (<5.4.0) and special treatment for EMIS

Philippe 27/11/2018: LFI2CDF: correct problems when reading files generated with older versions (tested on 5.3.1 files)

Philippe 10/04/2018: lfi2cdf: take into account previous commits on dimension variables + bug correction on NKMAX

* treat more correctly datetime variables from LFI files
* pass HPROGRAM_ORIG at closing and not opening of file

* improvements
* split option works again

Philippe 16/03/2018: lfi2cdf: remove file suffix from hinfile and houtfile to manage more cleanly filenames