PIM-1298 : add form subscriber to bind product to group
PIM-1298 : add grid that allow to select and associate products to a group
PIM-1298 : change mapping between groups and products (many to many) and
add related methods
PIM-1268 : add subscriber to ensure product binding
PIM-1268 : fix flash messages issues
PIM-1298 : move grid out of form to avoid to display "there are unsaved
changes" notice when we use grid filters