Fixes backwards compatibility issues where state was missing
Replaced the state dict by the request object in all cart modifiers
Merge branch 'cart_modifiers-fix-missing-state' into synthesa

Conflicts:
	CHANGELOG.rst
	shop/cart/modifiers/rebate_modifiers.py
Must also replace ``state`` against ``request`` in ``CartItem.update``
Merge branch 'cart_modifiers-fix-missing-state' into synthesa