Developer function

This function is made to update the fields of a structure, in case
some fields were not set in prior processes, for example wyou worked with
refine_Picks in earlier version and then afterwards you decide to define a
new field, instead of reprocessing the data you can just update fields to
missing field.
NB: it will NOT remove fields in USER structure, just add

Input:
STRUCT_USER: user structure
STRUCT_REF: reference structure

Output:
STRUCT_NEW: new structure with fields updated