[hooks/syncschema] do not crash on double removal of a constraint Some complicated migrations may entail a double constraint removal. It is not yet known whether this is a genuine cw bug or the result of a complicated migration story, but we should nevertheless not crash. Rather, emit a CRITICAL warning and proceed. Closes #3595309.

Add some entities
-----------------
As manager, you can access to entity creation forms by using the `site management`_ page.

.. _`site management`: manage

As regular user, the index page or the action box may propose some links to create entities according to the context.