Philippe 08/12/2016: IO:

* added pointers to the data in TFIELDDATA type
 (via array of pointers (one per mesh))
* used the previous array of pointers for some fields
  -> modif of ini files for them
* added IO_WRITE_FIELDLIST subroutine to write
  a series of fields (i.e. provided for output)
* moved INI_FIELD_LIST from INITIO_ll to INIT_MNH
* added new fields to TFIELDLIST