Replace use of 'uenc' and 'udec' functions from 'synnefo.util.text'
module with the 'smart_decode' and 'smart_unicode' functions from
'django.utils.encoding' module.

The uenc/udec functions depend on the locale category LC_CTYPE, which is not
appropriate for the Synenefo API. We explicitly use the
smart_unicode/smart_str functions to decode to unicode and encode to
bytestring objects, always using the utf-8 encoding.