* Implement shareable wishlists.

* Raise permission denied 403 instead of 404 if a user has no access to the wishlist.

* Change translation messages

The idea of splitting integration from unittests is good in theory
but leads to a lot of mental overhead. Besides whenever a tests
interacts with a database it isn't a unittest anyway.

Better to use filenames which are commonly used in the python word then
custom ones.