This commit adapts the business code to changes introduced by
the parent commit in order to keep the same behaviour as before.
All readonly=False fields will have to be checked afterwards to confirm
that the business case requires write access to the source field.
Extend new dynamic chatter to manage rating
when posting comment.
The model should inherit of rating.mixin and
its frontend chatter should allow rating to enjoy
star widget and rating card.
This is more generic : stats, rating, ... are manage
in one place (this module) for all document.