Enables to load a "ref_choice" object fom a list given by a "report" object
choice="character" A vector of character to choose within a droplist
the title of the box
Objects can be created by calls of the form
new("ref_list", listechoice, label).
Object of class "character"
Object
of class "character"
Object of class
"character"
Object of class "character"
Other referential objects: charge,ref_choice-method,
  ref_checkbox-class,
  ref_choice-class,
  ref_coe-class, ref_dc-class,
  ref_df-class,
  ref_horodate-class,
  ref_par-class,
  ref_parqual-class,
  ref_parquan-class,
  ref_period-class,
  ref_stage-class,
  ref_taxa-class,
  ref_year-class