Feature/coherent notification list

[nreynis]

All templates now get the same object and use the same parameter name.
Entities become JsonSerializable.

[nreynis]

I forgot to mention it, but there is a slightly breaking change in notification_list.html.twig:
The notification item in notificationList must now be accessed by key notification instead of index 0

[maximilienGilet]

Interesting feature, I think it will be implemented in a 3.0 version

Thanks for the contribution

[maximilienGilet]

Merged in dev branch.

Dev branch is for upcoming 3.0 version.

Thanks 👍