PropertySelector dialog, better display word/structures properties difference and selected properties difference

Current state does not differentiate the available and selected property lists.

Solution

• divide the available property list in 2 :
  • “word properties” FR “propriétés de mots”
  • “structures properties” FR “propriétés de structures”
• name the lists : “available properties/selected properties” FR “propriétés disponibles/propriétés sélectionnées”

(from redmine: issue id 2776, created on 2020/02/25 by Matthieu Decorde)