workshops/templatetags/breadcrumbs.py: Replace smart_unicode with smart_text

smart_text works on both Python 2 and 3 [1], while smart_unicode only
exists in Python 2 [2].

Also drop the smart_str import, since we weren't using it anywhere.

[1]: https://docs.djangoproject.com/en/1.7/ref/utils/#django.utils.encoding.smart_text
[2]: https://docs.djangoproject.com/en/1.7/ref/utils/#django.utils.encoding.smart_unicode
workshops/templatetags/breadcrumbs.py: Use logging for debugging output

The print statement is only in Python 2 (in Python 3 it's replaced by
the print() function).  In any case, this sort of debugging
information is best handled by logging [1].

[1]: https://docs.djangoproject.com/en/1.7/topics/logging/#using-logging
Merge pull request #87 from wking/breadcrumbs-python-3

Cleanups to get the breadcrumb templating working with Python 3