Add in documentation a dictionnary of major opfab concepts

[freddidierRTE]

The idea is to add in the documentation an explanation of major concept/word to know when using or developing

First list of concept to document :

• entity
• parentEntity
• process
• state
• process instance
• user
• card
• userCard
• chidCard
• perimeter
• group

This information is already present but not centralized

This new "Chapter" should be accessible easily