#16501. Add a ``unicode`` argument to models.SlugField and forms.SlugField.

Fix for [#16501](https://code.djangoproject.com/ticket/16501)
See also #1987 for an alternative solution
the unicode arg needs to be added to `deconstruct()` as well (I realize the PR was there first, but now it needs to be adapted). While at it, schema-editor tests should probably be added.