Fix product class admin

Slug fields need handling differently now that they are auto-slugfields.

Fixes #1233
Add echo statements to transifex script to aid debugging

It doesn't seem to be pushing successfully at the moment.
Transifex update
Fix travis transifex script

Required installing the client and skipping any syntax errors.
Merge branch 'master' of https://github.com/tangentlabs/django-oscar into project/mr